I N S T I T U T F Ü R M E E R E S K U N D E an d e r
Christian-Albrechts-Universität K i e l
Nr. 143 1 9 8 5
S K A R O V E R DATA REPORT I NORTH ATLANTIC SUMMER 1981
- B O A '81 -
by
Joachim Bauer, Jürgen F i s c h e r , Harry L e a c h , John Woods
3D1 Aö.l&W I iTH-'EeR- m
K o p i e n d i e s e r A r b e i t können bezogen werden b e i : D i r e k t o r d e r A b t e i l u n g R e g i o n a l e Ozeanographie I n s t i t u t für Meereskunde an der Universität K i e l Düsternbrooker Weg 20
D 2300 K i e l 1
ISSN 0341 - 8561
PREFACE
The NOA'81 SEA ROVER experiment was c a r r i e d out d u r i n g C r u i s e 76 of FS "Poseidon" between the A z o r e s , Greenland and the B r i t i s h I s l e s d u r i n g the summer of 1981.
The experiment was p a r t of a long-term r e s e a r c h programme designed t o i n v e s t i g a t e s t r u c t u r e s i n the s e a s o n a l boundary l a y e r . The s p e c t r a l range covers over t h r e e decades i n the h o r i z o n t a l ranging from the gyre s c a l e ( o r d e r 1000 km) to the mesoscale ( o r d e r 1 km) and i t i n c l u d e s f i n e s t r u c t u r e w i t h v e r t i c a l s c a l e s of more than one metre. Covering t h i s broad s p e c t r a l
range was o n l y p o s s i b l e w i t h the development of the "Seasonal and R e g i o n a l Ocean V a r i a b i l i t y E x p l o r e r " (SEA ROVER). A d e t a i l e d d e s c r i p t i o n of v a r i o u s p a r t s of the system can be found i n F i s c h e r et a l . (1985), Leach (1984) and Horch (1984).
A l t h o u g h these t e c h n i c a l r e p o r t s r e p r e s e n t the p r e s e n t s t a t u s of the system most of the p a r t s were a l r e a d y o p e r a t i o n a l i n 1981. A b r i e f d e s c r i p t i o n of the system i n c l u d i n g the data p r o c e s s i n g w i l l be g i v e n w i t h i n t h i s r e p o r t .
There were two main s c i e n t i f i c t a r g e t s :
(1) l a r g e - s c a l e v a r i a b i l i t y of the boundary l a y e r between the Azores (38° N) and 55" N,
(2) t h r e e - d i m e n s i o n a l mesoscale s t r u c t u r e of the p o l a r f r o n t near the Gibbs F r a c t u r e Zone.
A l t h o u g h the s c i e n t i f i c a p p l i c a t i o n s were d i f f e r e n t , the data sampling, p r o c e s s i n g and r e d u c t i o n of t h i s l a r g e data s e t was i d e n t i c a l f o r both p a r t s of the experiment, the p r o d u c t s a r e , however, presented s e p a r a t e l y a c c o r d i n g t o the s c i e n t i f i c o b j e c t i v e s .
W i t h i n t h i s r e p o r t we d e s c r i b e the experiment and d a t a p r o c e s s i n g , a s s e s s the e x p e r i m e n t a l e r r o r s and p r e s e n t a s e l e c t i o n of the p o s s i b l e p r o d u c t s from v a r i o u s stages of the data p r o c e s s i n g . Many of the d i a g n o s t i c techniques were developed t o a n a l y s e the B a t f i s h d a t a s e t c o l l e c t e d from RRS " D i s c o v e r y "
d u r i n g GATE (Woods and M i n n e t t , 1979; Leach, M i n n e t t and Woods, 1985). T h i s d a t a r e p o r t does not o f f e r s c i e n t i f i c i n t e r p r e t a t i o n of the d a t a . I t i s p o s s i b l e to g a i n some i n s i g h t i n the v a r i a b i l i t y encountered i n the s e a s o n a l boundary l a y e r from the s e l e c t i o n of p r o d u c t s d e r i v e d from r o u t i n e computer p r o c e s s i n g of the d a t a s e t .
33 5. ANALYSIS OF ERRORS
5.1 Measurement e r r o r s and c o r r e c t i o n s a p p l i e d d u r i n g d a t a p r o c e s s i n g 33 5.2 Numerical e s t i m a t i o n of u n c e r t a i n t i e s i n d e r i v e d q u a n t i t i e s . . . 38 5.3 Estimating the e r r o r s i n the o b j e c t i v e l y a n a l y s e d f i e l d s . . . . 41
5.4 Synoptic! ty • H H
6. STANDARD PRODUCTS - OFFSET PROFILES 57 6.1 P r o f i l e s from the Long S e c t i o n s 57 6.2 P r o f i l e s from the F r o n t a l Survey ( s e c t i o n s C311 and C312) . . . . 58
7. STANDARD PRODUCTS - SECTION PLOTS . . . 74
7.1 Long Sections 74 7.2 F r o n t a l Survey . 75 8. STATISTICS OF THE HYDROGRAPHIC DATA 86
8.1 Mean and standard d e v i a t i o n p r o f i l e s . . . 86 8.2 P r o b a b i l i t y d i s t r i b u t i o n s on s u r f a c e s of constant d e n s i t y . . . . 88
8.3 T-S Diagrams . . . . . . 89
9. ISOPYCNIC AND ISOBARIC MAPS FROM THE POLAR-FRONT SURVEY . . . 125
10. SURFACE CURRENTS . 136 10.1 Data a c q u i s i t i o n 136 10.2 D e v i a t i o n of the s t r e a m f u n c t i o n I n the s y n o p t i c - s c a l e survey a r e a 136
11. METEOROLOGICAL DATA 144
12. C0KL0SIO8S 149
13. REFERENCES . . . , r .
14. APPENDIX
C a l i b r a t i o n c o e f f i c i e n t s
1. INTRODUCTION
1.1 Alms of the experiment
The e x p l o r a t i o n of the thermohaline v a r i a b i l i t y i n the seasonal thermo- c l i n e as a f u n c t i o n of space and time i n d i f f e r e n t h y d r o g r a p h i c r e g i o n s of the N o r t h A t l a n t i c Ocean i s a long-term aim of the r e s e a r c h i n the R e g i o n a l Oceanography Department at I f M - K i e l . The "Seasonal and R e g i o n a l Ocean V a r i a b i l i t y E x p l o r e r " (SEA ROVER) measurement system was developed t o monitor t h e s e s t r u c t u r e s w i t h the best p o s s i b l e r e s o l u t i o n . The f i r s t use of t h i s system was i n the experiment c a l l e d NOA '81 d e s c r i b e d i n t h i s r e p o r t .
S c i e n t i f i c a l l y the experiment was designed f o r two major problems:
( a ) Long S e c t i o n s
The r e g i o n a l c l i m a t e of the ocean boundary l a y e r as a l i n k between the atmosphere and the i n t e r i o r of the ocean i s not yet w e l l understood.
The reason f o r t h a t i s the f a i l u r e of the too s c a r c e coverage of h y d r o g r a p h i c measurements, m a i n l y based on s t a t i o n d a t a , to r e s o l v e the r e g i o n a l , seasonal and i n t e r a n n u a l v a r i a t i o n s .
The SEA ROVER system i s a t o o l to improve data c o l l e c t i o n . I t measures p r o f i l e s of temperature, c o n d u c t i v i t y and h o r i z o n t a l v e l o c i t i e s a t the sea s u r f a c e and r e c o r d s n a v i g a t i o n and m e t e o r o l o g i c a l d a t a w h i l e the ship i s moving a t f u l l speed. The speed and the h i g h h o r i z o n t a l r e s o l u t i o n of the SEA ROVER system enable the s u r v e y i n g of l a r g e areas much more s y n o p t i c a l l y and w i t h b e t t e r r e s o l u t i o n than c l a s s i c a l s t a t i o n measure- ments do. Real-time data p r o c e s s i n g on board h e l p s t o reduce the enormous amount of d a t a .
I t i s planned to use the ready-processed data set to study the system atmosphere - mixed l a y e r - t h e r m o c l i n e , f o r c a l c u l a t i o n s of heat and f r e s h water budget and f o r i n v e s t i g a t i o n of s e a s o n a l c y c l e s of v a r i o u s parameters f o r example, mixed l a y e r depth, p o t e n t i a l v o r t i c l t y .
( b ) F r o n t a l S t r u c t u r e s
The mesoscale waveband i n the spectrum of o c e a n i c motion extends from t h e s p e c t r a l peak of s y n o p t i c - s c a l e motions (near the Rossby r a d i u s of d e f o r m a t i o n ) t o the s p e c t r a l peak of m i c r o s c a l e t u r b u l e n c e (at the Ozmldov s c a l e ) . I n the s e a s o n a l t h e r m o c l i n e , the mesoscale waveband
ranges from about 30 km to 30 cm. This s p e c t r a l band i n c l u d e s i n t e r n a l waves and the enstrophy cascade of i s o p y c n i c t u r b u l e n c e and f i n e s t r u c t u r e i n hydrographic p r o f i l e s . Mesoscale j e t s and f r o n t s a r e a key phenomenon i n these l a t t e r processes.
The aim of t h i s p a r t of the experiment was to survey the t h r e e - dimensional s t r u c t u r e of t h e r m o c l i n i c i t y , b a r o c l i n i c i t y , v e l o c i t y and p o t e n t i a l v o r t i c i t y to s p a t i a l and temporal r e s o l u t i o n s and a c c u r a c i e s commensurate w i t h the processes d e s c r i b e d by the computer models (Onken, Bleck and Woods, 1985).
Surveying mesoscale f r o n t s w i t h a r a p i d l y moving s h i p seems t o be the best s t r a t e g y to minimize the d i f f i c u l t i e s of i n t e r p r e t i n g the s t r u c t u r e s caused by non-synoptic or p o o r l y - r e s o l v i n g measurements.
The experiment should take p l a c e i n a r e g i o n where t h e r e l e v a n t q u a n t i t i e s show strong s i g n a l s , that means i n a r e g i o n w i t h the b e s t s i g n a l - t o - n o i s e r a t i o . Therefore we decided to choose the N o r t h A t l a n t i c P o l a r Front as a good t e s t s i t e f o r these s t u d i e s .
1.2 Experimental d e s i g n
For the experiment the f u l l c a p a b i l i t i e s of the measurement system were used. The towed f i s h u n d u l a t i o n i n the form of a saw t o o t h wave s h o u l d r e a c h c l e a r l y the mixed l a y e r and d i v e as deep as p o s s i b l e i n t o the s e a s o n a l thermocline w i t h a minimum wavelength t o r e s o l v e the expected steep temperature g r a d i e n t s . The s h i p should move at f u l l speed of about 5 m s-1 to improve s y n o p t i c i t y and save time d u r i n g measurements. The d a t a s h o u l d be recorded and processed c o n t i n u o u s l y .
( a ) Long Sections
For the i n v e s t i g a t i o n of the long s e c t i o n s the s h i p f o l l o w e d a l o n g standard t r a c k s whose choice had both t e c h n i c a l and s c i e n t i f i c r e a s o n s . They are the l i n k s between the f r o n t survey a r e a a t the p o l a r f r o n t , the supply base at the Azores and the home p o r t . They pass through the l o c a t i o n of the Ocean Weather Ships t o p r o v i d e a comparison of the d a t a w i t h the long-term measurements at the Ocean Weather S t a t i o n s . Repeated measurements along the same standard t r a c k s on r e t u r n t r i p s and i n d i f f e r e n t seasons and years should a l l o w i n v e s t i g a t i o n s about p e r s i s t e n c e of f e a t u r e s and seasonal and i n t e r a n n u a l v a r i a t i o n s .
(b) F r o n t a l Survey
A g e n e r a l survey p a t t e r n was designed to l o c a l i z e the s y n o p t i c - s c a l e s t r u c t u r e s , meanders and eddies of the N o r t h A t l a n t i c P o l a r F r o n t and t o f i n d a r e g i o n w i t h h i g h t h e r m o c l i n i c i t y , which i s d e f i n e d as the h o r i z o n t a l temperature g r a d i e n t on an i s o p y c n i c s u r f a c e . Then, f o c u s s i n g i n on t h a t r e g i o n , a high r e s o l u t i o n survey, which should r e s o l v e the mesoscale s t r u c t u r e s and c u t the f r o n t as many times as the a v a i l a b l e s h i p - t i m e a l l o w s , should be made. I n order to c o n t r o l the experiment, r e a l - t i m e graphs of the t h e r m o c l i n i c i t y s i g n a l should be used t o p r e d i c t the o r i e n t a t i o n of the f r o n t f o r the f o l l o w i n g s e c t i o n .
The towed f i s h u n d u l a t i o n i n form of a sawtooth wave should cover the upper 80 metres of the s t r u c t u r e s w i t h a minimum wavelength to r e s o l v e t h e expected h i g h t h e r m o c l i n i c i t y . The s h i p ' s speed was aimed t o be about 5 m s~ 1 i n order to minimize the e f f e c t of n o n - s y n o p t i c i t y I n t h e measurements.
1.3 E x p e r i m e n t a l s i t e and oceanographic c o n d i t i o n s
Our Long S e c t i o n s range from the Azores t o about 55° N from the a n t i - c y c l o n i c S u b t r o p i c a l Gyre w e l l i n t o the c y c l o n i c S u b a r t i c Gyre, where the P o l a r Front i s the boundary between these g y r e s , and from t h e Azores to the E n g l i s h Channel.
Both s e c t i o n s should i n t e r s e c t the s t r e a m l i n e s of the N o r t h A t l a n t i c Gyre ( D i e t r i c h , 1969). The mass t r a n s p o r t a c r o s s the Azores - Greenland s e c t i o n i s c o n c e n t r a t e d i n the r e g i o n of the P o l a r F r o n t o t h e r w i s e known as the N o r t h A t l a n t i c C u r r e n t , between 48° N and 51° N, whereas the Azores - E n g l i s h Channel s e c t i o n i s expected t o c r o s s the v a r i o u s branches of the r e c i r c u l a t i o n between the Azores and the European c o n t i n e n t ( D i e t r i c h e t a l . , 1980).
Both s e c t i o n s c r o s s the z e r o l i n e of the net annual water f l u x r e s u l t i n g from p r e c i p i t a t i o n minus e v a p o r a t i o n (Baumgartner and R e i c h e l , 1975).
A l o n g the Azores - E n g l i s h Channel s e c t i o n the net annual heat f l u x through the s u r f a c e i s n e a r l y z e r o w h i l e the Azores - Greenland s e c t i o n i n t e r s e c t s the a x i s o f maximum heat l o s s (Budyko, 1974),
The Azores - Greenland s e c t i o n f o l l o w s the t r a c k of the long h y d r o c a s t s e c t i o n measured d u r i n g the I n t e r n a t i o n a l G e o p h y s i c a l Year ( D i e t r i c h , 1969).
A recent summary of the seasonal and r e g i o n a l v a r i a t i o n a l o n g our s e c t i o n s can be found i n the I s o p y c n i c A t l a s of the N o r t h A t l a n t i c Ocean (Bauer and woods, 1984) which was d e r i v e d from the well-known Robinson-Bauer-Schroeder A t l a s (1979). The general s t r u c t u r e d u r i n g J u l y and August Is a w e l l - developed seasonal p y c n o c l i n e w i t h a s h a l l o w mixed l a y e r .
Winter mixing reaches deeper than 150 m i n the whole r e g i o n we s u r v e y e d . That means that the water column i n the depth range of the towed f i s h a l l l i e s w i t h i n the seasonal p y c n o c l i n e .
1.4 Sonderforschungsbereich 133 - "Warm Water Sphere of the A t l a n t i c "
Our work i n c l u d i n g the i n v e s t i g a t i o n of l a r g e - s c a l e s t r u c t u r e s i n the seasonal thermocline as w e l l as f r o n t a l s t r u c t u r e s can be seen i n the c o n t e x t of the long running "Warm Water Sphere" c o o p e r a t i v e r e s e a r c h programme (Sonde rforschungs be r e i c h ) funded by the Deutsche Forschungsgemeinschaft (German Research C o u n c i l ) . The aim of t h i s programme i s t o g a i n some i n s i g h t i n t o the dynamics and thermodynamics of the N o r t h A t l a n t i c , the t r a n s p o r t s of heat and mass from the western b a s i n a c r o s s the M i d - A t l a n t i c Ridge i n t o the e a s t e r n b a s i n , and the r e c i r c u l a t i o n i n the s u h t r o p i c s .
Although many groups p a r t i c i p a t e i n t h i s programme the i n t e r a c t i o n s w i t h the f o l l o w i n g groups are e s p e c i a l l y r e l e v a n t to our work:
S a t e l l i t e images of sea s u r f a c e temperature at the P o l a r F r o n t w i l l h e l p us to I d e n t i f y regions of s t r o n g t h e r m o c l i n i c i t y and g i v e some h i n t of the time s c a l e s of the observed s t r u c t u r e s (Hardtke and Meincke, 1984). S u r f a c e f l u x e s a f t e r Isemer and Hasse (1985) based on Bunker's data w i l l help us to i n t e r p r e t the l a r g e - s c a l e v a r i a t i o n of the s e a s o n a l t h e r m o c l i n e .
From long s e c t i o n s w i t h deep CTD-stations along the M i d - A t l a n t i c R i d g e (Meincke and Sy, 1983) the maximum depth of w i n t e r m i x i n g can be e s t i m a t e d by the "theraoclloicity elbow" method (Woods, 1985). D r i f t e r t r a j e c t o r i e s (Krauss and Meincke, 1982; Krauss and Käse, 1984) w i l l be used t o i d e n t i f y the seasonal catchment area of the water b e i n g advected through our a r e a .
1.5 P u b l i c a t i o n s and Reports
Bauer, J . and J.D. Woods (1984) I s o p y c n i c A t l a s of the N o r t h A t l a n t i c Ocean.
I f M K i e l B e r i c h t e Nr. 132.
The N o r t h A t l a n t i c p a r t of the n u m e r i c a l a t l a s produced by M. Robinson, E. Schroeder and R. Bauer (1979) from NODC data was used t o present the annual c y c l e of the hydrography on d e n s i t y s u r f a c e s . Monthly mean tempera- t u r e s were combined w i t h annual mean s a l i n i t i e s to c a l c u l a t e pseudo-monthly mean d e n s i t i e s .
The f i r s t p a r t presented monthly mean maps of the d i s t r i b u t i o n of p r e s s u r e , temperature and s a l i n i t y on v a r i o u s d e n s i t y s u r f a c e s .
V e r t i c a l s e c t i o n s i n i s o p y c n i c c o o r d i n a t e s were presented i n p a r t two.
They f o l l o w the standard s h i p ' s t r a c k s of the SFB-133 TP-B1: Azores - Greenland and Azores - E n g l i s h Channel.
F i s c h e r , J . , C. Meinke, P. J . M i n n e t t , V. Rehberg and V. S t r a s s (1985) A d e s c r i p t i o n of the I n s t i t u t für Meereskunde S c h l e p p f i s c h - S y s t e m . T e c h n i s c h e r B e r i c h t N r . 1, 2. A u f l a g e .
T h i s i s a d e t a i l e d t e c h n i c a l d e s c r i p t i o n of the mechanics, e l e c t r o n i c s and software of the S c h l e p p f i s c h - s y s t e m . T h i s r e p o r t i n c l u d e s a l s o an o p e r a t i n g manual f o r the use of the S c h l e p p f i s c h (towed f i s h ) and the b a s i c CTD d a t a p r o c e s s i n g f o r q u i c k - l o o k d a t a . Although t h i s i s a d e s c r i p t i o n of the present c o n f i g u r a t i o n of the system (1985), i t i s s t i l l r e l e v a n t f o r the 1981 s t a t e .
F i s c h e r , J . , H. Leach and J.D. Woods (1985) S y n o p t i c - s c a l e s t r u c t u r e s i n the s e a s o n a l t h e r m o c l i n e a t the N o r t h A t l a n t i c P o l a r F r o n t ,
( i n p r e p a r a t i o n )
T h i s i s a d e s c r i p t i o n of s y n o p t i c - s c a l e s t r u c t u r e s a t t h e North A t l a n t i c P o l a r Front measured w i t h the SEA ROVER system. T h i s paper draws a t t e n t i o n t o t h e s i m i l a r i t i e s between hydrographic data i n t h e s e a s o n a l t h e r m o c l i n e and sea s u r f a c e c u r r e n t s . Derived q u a n t i t i e s such as r e l a t i v e v o r t i c i t y and s p a c i n g between i s o p y c n a l s show s i g n i f i c a n t c o r r e l a t i o n s .
Horch, A. (1984) Eine Beschreibung der NOVA-Software für S c h l e p p f i s c h - experimente.
Technischer B e r i c h t Nr. 5, 2. A u f l a g e .
This i s a t e c h n i c a l report about the CTD-data p r o c e s s i n g and e d i t i n g on the shipboard minicomputer "N0VA-4C". The second e d i t i o n d e s c r i b e s the s t a t e of the software i n 1984, but i n c l u d e s the 1981 programs, ( i n German)
Leach, H. (1984) Eine Beschreibung des w i s s e n s c h a f t l i c h e n N a v i g a t i o n s s y s t e m s des FS "Poseidon".
Technischer B e r i c h t Nr. 2, 2. A u f l a g e .
This i s a d e s c r i p t i o n of the s c i e n t i f i c n a v i g a t i o n system based on an HP-1000 minicomputer, which was used i n 1981 on board FS " P o s e i d o n " . T h i s system i s the b a s i c t o o l f o r measuring sea s u r f a c e c u r r e n t s by u s i n g both absolute and r e l a t i v e n a v i g a t i o n . The second e d i t i o n d e s c r i b e s the s t a t e of the system i n 1984, but the main concept remains unchanged.
Leach, H. (1985) The a n a l y s i s of c u r r e n t s measured from a moving s h i p i n the region of the North A t l a n t i c P o l a r F r o n t ,
(submitted)
Ship d r i f t measurements were used t o c a l c u l a t e sea s u r f a c e c u r r e n t s independently from the hydrographie data. By u s i n g the r e l a t i v e v o r t i c i t y , which was derived from the o b j e c t i v e l y analysed c u r r e n t f i e l d , i t was p o s s i b l e to c a l c u l a t e the surface s t r e a m f u n c t i o n . S y n o p t i c - s c a l e meanders were the dominant f e a t u r e s i n the streamf u n c t i o n and some s i m i l a r i t i e s w i t h
the thermohaline s t r u c t u r e s have been observed.
2. INSTRUMENTATION - The SEA ROVER
2.1 The towed u n d u l a t i n g CTD-system as a concept
The i n v e s t i g a t i o n of processes i n the upper ocean w i t h s t r o n g v a r i a b i l i t y i n space and time, such as eddies and f r o n t s , set a s p e c i f i c a t i o n f o r the measurement system, which i s not or not s a t i s f a c t o r i l y f u l f i l l e d by conven-
t i o n a l p r o f i l i n g systems.
For s t u d y i n g such processes the measurement system should a l l o w f o r s y n o p t i c ! t y combined w i t h h i g h r e s o l u t i o n i n the space and time s c a l e s . These s c a l e s cover a broad s p e c t r a l range i n both space and time. High accuracy and long-term s t a b i l i t y of the c a l i b r a t i o n of the sensors i s another important requirement.
Q u a s i - s y n o p t i c measurements can only be obtained from a moving s h i p , u s i n g f r e e f a l l probes (XBT's, XSTD's) o r towed, u n d u l a t i n g systems.
I n order t o d e s c r i b e the k i n e m a t i c s and the dynamics of the ocean a t l e a s t temperature and s a l i n i t y as a f u n c t i o n of depth have t o be measured.
These are the u s u a l sensors of a normal CTD.
I n c o n t r a s t to any p r o f i l i n g from a s t a t i o n a r y or s l o w l y d r i f t i n g s h i p , where a " t r u e " v e r t i c a l p r o f i l e i s o b t a i n e d , a towed system w i l l g i v e the parameters as a f u n c t i o n of the v e r t i c a l and h o r i z o n t a l c o o r d i n a t e s depending on t h e s h i p ' s speed and t h e descent/ascent r a t e of the system. T h i s e f f e c t may d i s t o r t the measured parameter f i e l d a c c o r d i n g t o the i n c l i n a t i o n of the p r o f i l e . High v e r t i c a l speeds w i l l minimize t h i s d i s t o r t i o n , but some- times a c o r r e c t i o n w i l l be n e c e s s a r y , which i s o n l y p o s s i b l e i f the p o s i t i o n i n g of the system i s v e r y a c c u r a t e .
The q u i n t e s s e n c e of a l l these requirements l e d to a system, which i s d e r i v e d from the Bedford I n s t i t u t e " B a t f i s h " ( D e s s u r e a u l t , 1976) and the IOS (Wormley) "Sea Soar" ( C o l l i n s et a l . , 1983). I t s h o u l d c a r r y a h i g h r e s o l u t i o n CTD w i t h f a s t response sensors to reduce the time l a g e f f e c t s caused by the h i g h p e n e t r a t i o n speed of t h e f i s h . A c c u r a t e n a v i g a t i o n w i t h the p o s s i b i l i t y o f c a l c u l a t i n g p o s i t i o n s r e l a t i v e t o a moving body of water w i l l complete t h e system, e s p e c i a l l y i f the experiment r e q u i r e s q u a s i -
" L a g r a n g i a n " c o o r d i n a t e s (Woods and M i n n e t t , 1979).
The SEA ROVER system was used f o r the f i r s t time d u r i n g the experiment N0A*81. A c c o r d i n g to the requirements d e s c r i b e d above, the system has t h r e e main t a s k s :
1) Continuous CTD data sampling w i t h a towed system.
2) C o l l e c t i o n of n a v i g a t i o n data d u r i n g the experiment i n a b s o l u t e and r e l a t i v e c o o r d i n a t e s .
3) Real-time data p r o c e s s i n g .
2.2 The IfM towed f i s h system
One key p a r t of the system developed a t the I n s t i t u t für Meereskunde K i e l (IfM) i s a towed d e p t h - c o n t r o l l e d underwater v e h i c l e , which i s a f u r t h e r development of the "Sea Soar" designed a t the I n s t i t u t e of Oceanographic Sciences (IOS) i n Wormley, England, which i s i t s e l f a development of the o r i g i n a l Hermes/Gulldline " B a t f i s h " ( D e s s u r e a u l t , 1976).
The main components of t h i s system a r e the v e h i c l e w i t h i t s h y d r a u l i c s and underwater e l e c t r o n i c s , a CTD-probe and the c o n t r o l u n i t on board the s h i p . For i l l u s t r a t i o n of the v a r i o u s t a s k s of the system see f i g u r e 2.2.1.
The nose, t a i l - p l a n e and wings of the towed f i s h are made from f i b r e - glass-reinforced p o l y e s t e r r e s i n , whereas the f u s e l a g e i s c o n s t r u c t e d from s t a i n l e s s s t e e l . The l a t t e r holds the wing a x l e and the f i t t i n g s f o r the e l e c t r o n i c s pressure v e s s e l s and the h y d r a u l i c s u n i t . The wings are mounted on a h o r i z o n t a l a x l e so that t h e i r angle r e l a t i v e t o the f u s e l a g e can be varied to cause the f i s h t o climb or d i v e .
In order to reduce r o l l i n g of the f i s h , a s t a b i l i z i n g f i n i s f r e e l y h i n g e d at the t a i l ( D e s s u r e a u l t , 1976) (see f i g u r e 2.2.3).
The f i s h c o n t a i n s two p r e s s u r e v e s s e l s , one f o r the c o n t r o l e l e c t r o n i c and the other being the CTD underwater u n i t . The h y d r a u l i c s are c o n t a i n e d i n a c y l i n d r i c a l o i l b a t h which i s p r e s s u r e - e q u a l i z e d w i t h the s u r r o u n d i n g s . The control e l e c t r o n i c s are based on those developed a t the F o r s c h u n g s - anstalt für W a s s e r s c h a l l - und Geophysik der Bundeswehr, M e l (FWG). T h i s unit performs f o u r tasks:
(1) wmitorlng the parameters which d e s c r i b e the c o n d i t i o n of the f i s h , i . e . depth, wing a n g l e , r o l l and p i t c h angles*,
(2) t r a n s m i t t i n g these d a t a t o the c o n t r o l u n i t on board the towing s h i p ; (3) r e c e i v i n g and decoding the command s i g n a l from the c o n t r o l u n i t ;
(4) generating the analogue signal to control the Moog-servo-valve which determines the wing wvement.
A separate strain-gauge p r e s s u r e c e l l i s used to monitor the depth of the f i s h , i n order t o enable t h e f i s h t o be c o n t r o l l e d i n d e p e n d e n t l y w i t h o u t r e c o u r s e to the p r e s s u r e s i g n a l from the CTD. T h i s m o d u l a r i z a t i o n of the system, making the f i s h independent of the p a y l o a d , proved u s e f u l i n p r a c t i c e p a r t i c u l a r l y d u r i n g the development phase.
A v e r y durable h y d r a u l i c system (based on t h a t used i n the IOS Sea Soar:
C o l l i n s et a l . , 1983) d r i v e s the t i l t i n g of the wings. T h i s system i s designed to a l l o w long tows ( a p p r o x i m a t e l y 1000 hours between r o u t i n e s e r v i c e s ) , and due t o the h i g h o i l p r e s s u r e of up t o 7 MPa, an immediate response to the command s i g n a l generates sharp t u r n i n g p o i n t s i n t h e f i s h p r o f i l e s . The o i l p r e s s u r e i s p r o v i d e d by a pump d r i v e n by an i m p e l l e r a t
the back of the f i s h turned by t h e water f l o w i n g p a s t i t .
The g e n e r a t i o n and t r a n s m i s s i o n of the command s i g n a l i s one task of the c o n t r o l system on board the s h i p , which a l s o monitors the a t t i t u d e of t h e f i s h and uses the data s u p p l i e d by the payload (CTD-probe), t o c a l c u l a t e s a l i n i t y and d e n s i t y . The system d e s c r i b e d and i t s software i s developed from those of the F W G - c o n t r o l l e r . There are two o p e r a t i n g modes, manual and a u t o m a t i c . I n manual mode, used o n l y d u r i n g deployment and recovery of the f i s h , the wing angle i s a d j u s t e d by the s e t t i n g of a hand-operated p o t e n t i o m e t e r . I n automatic mode, the c o n t r o l l e r guides the f i s h along a sawtooth t r a c k between maximum and minimum depth w i t h a constant d i v e - and c l i m b - r a t e , a l l chosen by the o p e r a t o r . The c o n t r o l a l g o r i t h m t r i e s t o minimize any d e v i a t i o n from the d e s i r e d t r a c k . I n order t o c o n t r o l t h e f i s h i n d e p e n d e n t l y from the payload (CTD) a separate p r e s s u r e gauge i s used, which i s p a r t of t h e c o n t r o l e l e c t r o n i c s .
The f i s h was towed on a 10 mm diameter s i n g l e core towing c a b l e , f i x e d by a b r i d l e t o the f i s h . T h i s cable was u n f a i r e d and has a nominal b r e a k i n g s t r a i n of s i x tonnes. A l l s i g n a l t r a n s f e r to and from the underwater u n i t and the c u r r e n t supply was c a r r i e d a l o n g t h i s c a b l e . Three frequency bands were used, one f o r the c o n t r o l s i g n a l t o the f i s h , one f o r t h e f i s h p a r a - meter to the s h i p and one f o r the CTD d a t a to the s h i p . The c a b l e was p a i d out from t h e towing winch on FS " P o s e i d o n " u s i n g t h e A-Frame and the G e o l o - g i c a l Boom as shown i n f i g u r e 2.2.2. I n normal towing o p e r a t i o n t h e boom i s i n i t s r e s t i n g p o s i t i o n . Only d u r i n g deployment and r e c o v e r y the boom i s extended and the c a b l e removed from t h e snatch b l o c k on the p o r t s i d e of t h e A-Frame.
The payload i n 1981
The CTD-probe i n the towed f i s h was a s l i g h t l y m o d i f i e d ME-Kompakt-Sonde from "Meerestechnik E l e k t r o n i k GmbH, Trappenkamp". I n o r d e r t o r e s o l v e s m a l l - s c a l e temperature and s a l i n i t y g r a d i e n t s , t h e sensors s h o u l d have h i g h r e s o l u t i o n and accuracy, and a q u i c k response. F o r q u a l i t y c o n t r o l o f the data two thermometers and c o n d u c t i v i t y c e l l s p l u s the p o s s i b l i t y t o d i s p l a y the measured d i f f e r e n c e s were needed. Table 1 shows the s p e c i f i c a t i o n s of the sensors as g i v e n by the manufacturers.
Table 1 - Table of sensor s p e c i f i c a t i o n ME-Multisonde
PA1AMETKR SPECIFICATION
PRESSURE P r i n c i p l e Range R e s o l u t i o n Accuracy
: Strain-gauge p r e s s u r e c e l l : 0 - 600 dbar
: 0.01 dbar : 0.25 % o f range TEMPERATURE P r i n c i p l e
Range R e s o l u t i o n Accuracy
: P l a t i n u m r e s i s t a n c e : -2 - +40 °C
: 0.001 °C : 0.005 °C CONDUCTIVITY P r i n c i p l e
Range R e s o l u t i o n Accuracy
: Symmetric e l e c t r o d e c e l l : 5 - 5 5 ttS/ca
: 0.001 mS/cm : 0.005 ms/cra
Temperature and c o n d u c t i v i t y sensors were mounted i n p a i r s on the lower t a i l plane of the f i s h , f i g u r e 2.2.3, whereas the s t r a i n - g a u g e p r e s s u r e c e l l i s directly fixed to the CTD-vessel i n s i d e the towed f i s h . The sampling r a t e , which was used i n the HOA'81 experiment was 16 c y c l e s per second, e q u i v a l e n t to a time interval of 62.5 ms between each d a t a cycle, each of which consists of one pressure, two temperature and two c o n d u c t i v i t y Measure- ments.
The raw data {torn the CTD-probe were c o n v e r t e d i n t o 1 6 - M t words by the microprocessor controller and then a r c h i v e d on a n i n e - t r a c k d i g i t a l t a p e , followed by t r a i l e r information about time and d i v e - c l i m b o r i e n t a t i o n after every 50 data cycles.
To allow quick-look analysis of the d a t a , e v e r y •W t a <i.«.
one cycte par second) was transformed into p h y s i c a l u n i t s , m A s a l i n i t y and
d e n s i t y were c a l c u l a t e d . A l l v a l u e s were d i s p l a y e d on the f r o n t panel of the c o n t r o l l e r , and a subsample, chosen by the o p e r a t o r , was a v a i l a b l e on analogue output channels.
2.3 The "Poseidon" N a v i g a t i o n System
The NOA'81 e x p e d i t i o n was the f i r s t e x p e d i t i o n i n which the "Poseidon"
n a v i g a t i o n system was used to c o l l e c t and s t o r e n a v i g a t i o n d a t a . T h i s system s e r v e s e x c l u s i v e l y as a s c i e n t i f i c a i d and i s not used f o r the r o u t i n e s h i p n a v i g a t i o n . The system i s based on a H e w l e t t - P a c k a r d HP1000 minicomputer to which many of the s h i p ' s n a v i g a t i o n a l i n s t r u m e n t s are i n t e r f a c e d as shown i n f i g u r e 2.3.1. During t h i s c r u i s e t h e computer was r u n n i n g under a v e r s i o n of the RTE-MIII o p e r a t i n g system w i t h 64K memory. T h i s a l l o w e d a maximum of t h r e e p a r t i t i o n s which i n t u r n l i m i t e d the number of programs which c o u l d run i n p a r a l l e l to t h r e e . So t h r e e t a s k s could be performed i n r e a l - t i m e : f i r s t the a c q u i s i t i o n of s a t e l l i t e - n a v i g a t i o n p o s i t i o n s from the Magnavox MX1105, second the i n t e g r a t i o n of the s h i p ' s p o s i t i o n r e l a t i v e t o the water u s i n g the Colnbrook e l e c t r o m a g n e t i c l o g , and t h i r d d i s p l a y i n g the n a v i g a t i o n i n alphanumeric and g r a p h i c form on the system's g r a p h i c t e r m i n a l s .
Spot values of a l l the a v a i l a b l e n a v i g a t i o n a l parameters were p r i n t e d out and s t o r e d on d i s c every two minutes. The d a t a on d i s c were then t r a n s f e r r e d to magnetic tape two or t h r e e times a day as necessary f o r merging w i t h the d a t a from the towed f i s h .
The e l e c t r o m a g n e t i c l o g was c a l i b r a t e d o f f the Azores on I S t h J u l y 1981 u s i n g a d r i f t i n g radar-buoy w i t h a s a i l c e n t r e d at the depth of the l o g
( c a . 4.5 m). The f o r e - a f t and p o r t - s t a r b o a r d components were c a l i b r a t e d s e p a r a t e l y . The d e t a i l s of the method used are c o n t a i n e d i n Leach, 1984.
T h i s was a t h i r d set of c o e f f i c i e n t s o b t a i n e d which were a c c o r d i n g l y s t o r e d i n a f i l e named #KAL3.
Table 2.3.1 l i s t s the programs used d u r i n g the NOA '81 e x p e d i t i o n .
Table 2.3.1 - Programs used on the "Poseidon" n a v i g a t i o n system d u r i n g N0A»81
a c q u i s i t i o n of s a t e l l i t e n a v i g a t i o n d a t a SATNA
EML0G/EML02(TE) a c q u i s i t i o n and i n t e g r a t i o n of e l e c t r o m a g n e t i c l o g s i g n a l
PL0TT/PL0T2(TE)/PL0T3(TE) output of alphanumeric and g r a p h i c data t o t e r m i n a l s
CHK2M c o r r e c t i o n of 2-minute data on d i s c H2MTP
H2MTQ } t r a n s f e r of 2-minute data from d i s c t o tape H2MTR
EMKAL c a l i b r a t i o n of e l e c t r o m a g n e t i c l o g DECCA/DECC2(TE) Decca n a v i g a t i o n
Note: Those programs f o l l o w e d by the l e t t e r s (TE) r a n under timed e x e c u t i o n and were scheduled by the o p e r a t i n g system whereas the o t h e r s were f r e e - r u n n i n g .
2.4 Data a c q u i s i t i o n and r e a l - t i m e m o n i t o r i n g
To conduct an experiment f o r mesoscale f r o n t a l s t u d i e s means not o n l y t o have a s u i t a b l e measurement system, but to o b t a i n i n f o r m a t i o n about the s p a t i a l s t r u c t u r e of the phenomenon i n almost r e a l - t i m e . T h i s l e d t o the r e a l - t i m e data p r o c e s s i n g scheme, shown i n f i g u r e 2.4.1. " R e a l - t i m e " i n t h i s context means t o get the d e s i r e d r e s u l t s , f o r example, p l o t s of temperature d i s t r i b u t i o n on d e n s i t y s u r f a c e s , i n a time i n t e r v a l , which i s e q u i v a l e n t t o t h a t of data a c q u i s i t i o n . I n the f i r s t s t a g e , the raw f i s h data and the n a v i g a t i o n data were merged and i n t e r p o l a t e d t o the same time
i n t e r v a l . The data were then separated i n t o ascending and descending p r o f i l e s . For the r e a l - t i m e a n a l y s i s only the descending p a r t was used f o r f u r t h e r b l o c k averaging and t r a n s f o r m a t i o n t o p h y s i c a l u n i t s . I n a d d i t i o n s a l i n i t i e s and d e n s i t i e s were c a l c u l a t e d , and the r e s u l t i s s t o r e d on d i g i t a l t a p e .
I n the t h i r d stage the v a r i a b l e s were i n t e r p o l a t e d onto s t a n d a r d s u r f a c e s , e.g. temperature and pressure on constant d e n s i t y 1%} and d e n s i t y on temperature.
These products were p l o t t e d a f t e r w a r d s , t o a l l o w necessary d a t a a n a l y s i s .
In the Towed Fish
Sensors Pressure — Wing Angle- Pitch Roll
Sea Cabl
Pressure Temperature 1- Conductivity 1- Temperature 2- Conductivity 2-
C T D Underwater + Unit
Towed Fish Data Interfaces
Telemetry
F i s h E l e c t r o n i c s
Servo Valve
Strain Gauge
• Serial I/O O Parallel I/o
C T D Data CTD Signal
Filters Strain Gauge Interface
"ft*
Command sh Signal
I
RAM Data Buffers Signal
Command Signal Telemetry Program RAM E P R O M Maths Unit
C P U
Front Panel Controls and Displays
- O -
D/A and A / D Converters
Controller
T T V| K e y b o a r d
— 1 1 TI Printer
.Magnetic Tapes
^Analogue Plotters
F i g . 2.2.1: Sketch of the main components i n the towed f i s h system, i n c l u d i n g the f l o w of c o n t r o l s i g n a l s and s c i e n t i f i c d a t a .
F i g . 2.2.2: " S c h l e p p f i s c h " towing arrangement viewed from above on board FS " P o s e i d o n " u s i n g t h e towing winch (10 mm s i n g l e c o r e c a b l e ) , t h e g e o l o g i c a l boom and t h e A-Frame.
F i g . 2.2.3: F r o n t - and s i d e view of the towed f i s h , showing the main com- ponents of the f i s h and t h e s c i e n t i f i c sensor c o n f i g u r a t i o n d u r i n g the experiment NOA'81.
t
Clock Display
Qyro - Campa s s
Dacca Navigator
EM-Log.
Board Unit
Satellite Navigator Magnavox MX 1105
ex4Bit BCD parallel
Synchro
Optical Incremental Encoder
10 Bit parallel T
6 Channel analog
2 Channel analog
P U R P O S E B U I L T I N T E R F A C E
Clock
Compass Interface
Dacca Interface
EM-Log.
Interlace
M E A S U R E M E N T A N D C O N T R O L P R O C E S S O R
H P 2240 A
20mA Current Loop
H P 2 2 9 0 2 A DIGITAL INPUT
H P 2 2 9 0 2 A DIGITAL INPUT HP 22904 A DIGITAL O U T P U T
HP 2 2900 A A N A L O G U E
INPUT
H P - I B
MINI C O M P U T E R H P 2113 B
H P 12966A I N T E R F A C E
H P 1 2 9 6 6 A I N T E R F A C E
H P 5 9 3 1 0 B H P — I B I N T E R F A C E
H P 12531C B U F F E R E D T T Y I N T E R F A C E
HP 13181A I N T E R F A C E
H P 12735 A I N T E R F A C E
T E R M I N A L 1 H P 2 6 4 8 A
T E R M I N A L 2 H P 2 6 4 8 A
LINE P R I N T E R HP9876 A
M A G N E T I C T A P E HP 7970 B
F L O P P I E S . HP 9885 M / S
P i g . 2.3.1: B l o c k d i a g r a m of t h e s c i e n t i f i c n a v i g a t i o n system, i n c l u d i n g d a t a s o u r c e s , main computer and d a t a s t o r a g e p e r i p h e r a l s .
R E A L T I M E DATA P R O C E S S I N G
FLOW DIAGRAM
Time in % of data acquisition interval
Merging data
U A . X . Y . R T ^ ClTs A .
<mi
Separation of ascending and descending profiles Block averaging
Transformation of raw-data to physical values Calculation of derived variables t,f,A,X,Y,P,T1,C1,T2,C2, Sv S2,ort1, at2
Interpolation on to isopleths
!oj"= const. (3 isopycnals) PI
IO"t= const.
(3 isopycnals)
^It » const. (7 isotherms )
(DK'Mp
Section plots
^ lfft= const., ^ lo~t- const. , IT- const.
100
40
30
15
15
F i g . 2.4.1: Blockdiagram o f on-board r e a l - t i m e data p r o c e s s i n g and t i m i n g diagram. The f i n a l output was used t o c o n t r o l the survey p a t t e r n .
3. THE EXPERIMENT
The long-term f i e l d programme was designed to make a s e r i e s of long s e c t i o n s measuring the temperature, s a l i n i t y and d e n s i t y f i e l d i n the seasonal boundary l a y e r during d i f f e r e n t seasons of the y e a r . A d e t a i l e d study of the three-dimensional thermohaline v a r i a b i l i t y a t the N o r t h A t l a n t i c P o l a r Front was incorporated i n these long s e c t i o n s .
The u n d u l a t i o n of the f i s h was set to a sawtooth waveform w i t h t u r n i n g p o i n t s close to the surface and at 80 metres. A s h i p ' s speed of about 4 - 5 metres per second and a mean ascent/descent r a t e of 2 metres per second gave a wavelength of about 500 metres. A t y p i c a l example of the t r a c k i s shown i n f i g u r e 3.1.
The data sampling r a t e (16 data c y c l e s per second) gave a mean v e r t i c a l r e s o l u t i o n of 12.5 cm.
3.1 The Long Sections
For the long s e c t i o n s we chose two standard t r a c k s which were p l a n n e d t o be surveyed i n d i f f e r e n t years and a t d i f f e r e n t seasons ( f i g u r e 3.1.1).
The Azores - E n g l i s h Channel s e c t i o n s t a r t s a t the s h e l f edge of the western approaches to the E n g l i s h Channel a t about 48*15' N, 10*40' W, passes through the p o s i t i o n of Ocean Weather Ship "R" a t 47* N, 17* W and
f i n i s h e s at the e a s t e r n end of the Azores* i s l a n d Sao M i g u e l a t 37°50' N, 24*50' W.
The s e c t i o n Azores - Greenland s t a r t s at the western end of Sao M i g u e l a t 37*50' N, 25*55' W heading towards the southern end of Greenland, a v o i d s the d i r e c t pass over of the r e l a t i v e l y s h a l l o w Chaucer Bank at 43° N, 29" W, by passing through the p o i n t 43* N, 30* W and passes Ocean Weather Ship "C"
a t 52*40' N, 35*30' W and continues i n the same d i r e c t i o n u n t i l the 10 °C isotherm reaches the s u r f a c e , which was found i n 1981 a t 55* N, 37* W.
The high s p a t i a l r e s o l u t i o n covers a s p e c t r a l range from 2500 km which i s the l e n g t h of a standard s e c t i o n to the N y q u i s t wave l e n g t h o f 1 km, which was twice the d i s t a n c e between s i n g l e p r o f i l e s . With t h i s range g y r e - s c a l e , eddy-scale as w e l l as mesoscale s t r u c t u r e s are r e s o l v e d .
The depth range from 0 - 80 m i n c l u d e s the mixed l a y e r and the d i u r n a l thermocline and at l e a s t i n the summer the upper p a r t of the s e a s o n a l
t h e r m o c l i n e . As the system works at f u l l s h i p ' s speed of about 5 m s- 1 the measurements are as s y n o p t i c as reasonably p o s s i b l e . The h i g h data d e n s i t y ensures the observed s t r u c t u r e s a h i g h s t a t i s t i c a l s i g n i f i c a n c e .
The t i m e t a b l e of the 1981 e x p e d i t i o n allowed comparison of measurements of the same area i n a time range of s i n g l e days to 2 months ( f i g u r e 3.1.2).
The time i n t e r v a l between the northward and southward l e g of the A z o r e s - Greenland s e c t i o n i s only some days n o r t h of the P o l a r Front and about 2 weeks south of i t . The r e t u r n l e g from the Azores towards the E n g l i s h Channel (10th to 18th September) was made 2 months l a t e r than the outward l e g (14th t o 18th J u l y ) .
3.2 The P o l a r Front Survey
The area f o r the f r o n t a l survey was roughly f i x e d d u r i n g the long s e c t i o n B102 from the Azores to the outcrop of the 10 °C isotherm a t about 55" N.
The r e g i o n of s t r o n g e s t h o r i z o n t a l thermohaline c o n t r a s t was found near 51° N, 35° W i n the v i c i n i t y of OWS "C". This r e g i o n was thought t o be the edge of the warm water sphere, s e p a r a t i n g the r e l a t i v e l y warm water of about 15° C a t the s u r f a c e from the r e l a t i v e l y c o l d water w i t h 11 °C or l e s s . The sea s u r f a c e s a l i n i t y decreased from 35.4 x 10 t o l e s s than 34.8 x 10 w i t h i n 3 3 50 k i l o m e t r e s .
A set of two east-west s e c t i o n s (C301, C305 combined w i t h C303) each about 400 k i l o m e t r e s long ( f i g u r e 3.2.1) s h o u l d g i v e some i n f o r m a t i o n about the p r i n c i p l e s y n o p t i c - s c a l e s t r u c t u r e s i n t h i s r e g i o n . These s e c t i o n s form a n e a r l y r e c t a n g u l a r box of 400 km x 200 km, 5° W of the M i d - A t l a n t i c Ridge s o u t h of the Gibbs-Fracture-Zone.
A more d e t a i l e d study of the f r o n t a l s t r u c t u r e s was c a r r i e d out a t 51" N, 35° W. This p a r t of the experiment c o n s i s t s of 10 s e c t i o n s , each about 75 km l o n g and about 10 km a p a r t . These s e c t i o n s were o r i e n t a t e d almost p e r p e n d i c u l a r t o the a x i s of the f r o n t . U n f o r t u n a t e l y the o r i g i n a l o r i e n t a t i o n had to be changed a f t e r s e c t i o n C312 due to bad weather c o n d i t i o n s .
Table 3.1 shows a summary of a l l NOA'81 s e c t i o n s w i t h s t a r t and end p o s i t i o n , s t a r t and end time and the mean s h i p ' s heading.
I n a d d i t i o n to the s e c t i o n s , a deep (600 m) s e c t i o n w i t h c o n v e n t i o n a l CTD d i p s was c a r r i e d out to e x p l o r e the v e r t i c a l e x t e n s i o n of the observed f e a t u r e s .
Section
S t a r t of S e c t i o n
Day no. I Longitude I L a t i t u d e
(GMT) ( ÇW)
I
(N) Day no. (GMT)End of S e c t i o n
Longitude i L a t i t u d e
(W) J (N) O r i e n t a t i o n
B101 B101 B101 B102 B102 B102 B103 C301 C302 C303 C304 O305A C305B C305C C305D C306A C306B C307 C308A C308B C309 C310 C310A C311 C311A C312 C312A C313 C313A C314 C314A C315 C315A C316 C316A G317
m
195/0810 196/0932 202/1012 206/1303 207/0518 208/1300 209/0452 209/0930 210/1000 210/1420 210/1934 210/2110 211/0800 211/1330 211/1726 211/2134 212/0142 212/0841 214/0946 214/2010 215/0340 215/0436 215/0914 215/1002 215/1500 215/1542 215/2024 215/2106 216/0158 216/0222 216/0708 216/0752 216/1200 216/1236
11*28.02' 16*59.73»
25*56.42' 35*33.90' 37*04.02' 34*53.50' 31*00.22' 30*55.69' 37*04.36' 37*06.29*
35*54.65' 35*58.42' 33*26.16*
33*43.89' 34*44.45' 35*19.83' 35*53.96' 35*48.58' 35*21.05' 34*55.46' 35*49.00' 35*44.10»
35*00.09' 34*53.39' 35*39.45' 35*37.71' 34*39.73' 34*36.58»
35*40.96»
35*38.80' 34*34.92' 34*32.83' 35*29.12' 35*27.58»
48*29,94' 47*00.48' 37*50.32' 52*40.80' 55*04.02*
50*19.06' 50*15.67' 51*00.48' 51*11.51' 50*44.97' 50*45.69*
50*34.92' 50*39.04' 50*25.80' 50*28.04«
50*04.85' 50*33.02' 50*35.67' 50*19.61' 50*04.82' 50*38.13' 50*43.34' 50*14.57' 50*19.26' 50*45.25' 50*49.72' 50*35.52' 50*40.37' 50*58.03' 51*00.42"
50*45.39*
50*50.87' 51*03.96' 51*08.94*
50*50.16' 38*56.20'
199/0708 207/0518 208/1300 209/0452 209/0930 210/1000 210/1420 210/1934 210/2110 211/0800 211/1116 211/1726 211/2118 212/0412 212/0526 212/1052 214/1125 215/0340 215/0436 215/0914 215/1002 215/1500 215/1542 215/2024 215/2106 216/0158 216/0222 216/0708 216/0752 216/1200 216/1236 216/1802 220/0852 257/1042
24*56.55' 37*00.17' 34°53.50*
31*00.22' 30°55.69' 37*04.36' 37*06.29' 35*54.65' 35*58.42' 33*16.16' 33*38.94' 34*44.45' 35*18.89' 35*53.96*
35*30.55' 35*30.98' 35*08.02' 35*49.00' 35*44.10' 35*00.09*
34*53.39' 35*39.45' 35*37.71' 34*39.73*
34*36.58' 35*40.96' 35*38.80' 34*34.92' 34*32.83' 35*29.12' 35*27.58*
34*05.39' 25*55.48' 11*22.08*
37*51.43' 55*04.02' 50*19.06*
50*15.67*
51*00.48' 51*11.51' 50*44.97' 50*45.69*
50*34.92' 50*39.04' 50*25.21' 50*28.04' 50*05.01*
50*33.02*
50*19.96' 50*24.16' 50*11.25*
50*38.13' 50*43.34' 50*14.57' 50*19.26' 50*45.25' 50*49.72' 50*35.52*
50*40.37*
50*58.03*
51*00.42' 50*45.39' 50*50.87' 51*03.96*
51*08.94' 50*50.16' 38*00.21*
48*29.86'
OWS "R"
0WS "C"
northernmost point
"90 *"
"360°"
"270°"
"180°"
»90°..
"180°"
"9 0° . .
"235"
"270°"
"225°"
.111 "315*
}112A "135°"
1L2B "135°"
"315°" s e c t i o n
^50* t u r n i n g point
"135" s e c t i o n
•*25° t u r n i n g p o i n t
"315° s e c t i o n
•»25° t u r n i n g p o i n t
"110*" s e c t i o n 10° t u r n i n g p o i n t
"290 s e c t i o n
»10 t u r n i n g p o i n t '110°" s e c t i o n
~20° t u r n i n g p o i n t
"290°" s e c t i o n
•»20° t u r n i n g p o i n t
"108°" s e c t i o n
P o l a r Front - Azores Azores - Lands End
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
(1985)*
LISBON
1983
1981
B101
B121 *™
- 1984 S B1— — — " I
ib!2üriL-pws'ci
LANDS END
KIEL S E A R O V E R NE ATLANTIC SECTIONS
WINTER
S P R I N G
SUMMER
A U T U M N
F i g . 3.1.2: Seasonal d i s t r i b u t i o n of long SEA ROVER s e c t i o n s 1981 t o 1985.
The time of year i s presented versus the d i s t a n c e from the Azores (Sao M i g u e l ) a l o n g the standard s e c t i o n s . T h i n l i n e s i n d i c a t e SEA ROVER s e c t i o n s which do not f o l l o w the standard t r a c k s .
F i g . 3.2.1: Ship's t r a c k d u r i n g the f r o n t a l survey i n summer 1981.
4. PROCESSING AND REDUCTION OF HYDROGRAPRTC DATA
A flow diagram of the data p r o c e s s i n g and i t s products i s presented i n f i g u r e 4.1. The p r o c e s s i n g d e s c r i b e d i n t h i s chapter i s t h a t used on l a n d a f t e r the experiment.
4.1 CTD raw data r e c o r d i n g
The s i g n a l s from the p r e s s u r e sensor, the two temperature and the two c o n d u c t i v i t y sensors of the CTD-payload were d i g i t i z e d i n the underwater u n i t and w r i t t e n on tape i n b l o c k s of 256 1 6 - b i t words. 250 words c o n t a i n 50 c y c l e s w i t h raw numbers from the f i v e sensors s t o r e d a t the I n t e r v a l of 62.5 ms f o l l o w e d by a 6-word t r a i l e r c o n t a i n i n g the s t a r t time of the b l o c k and an up/down f l a g i n d i c a t i n g whether the f i s h was c l i m b i n g o r d i v i n g .
4.2 N a v i g a t i o n data r e c o r d i n g and c o r r e c t i o n
On t h e n a v i g a t i o n computer a permanent random access f i l e was arranged w i t h 720 r e c o r d s , one f o r each 2-minute i n t e r v a l of the day. Every 2 minutes
the f i l e was updated w i t h the c u r r e n t n a v i g a t i o n d a t a . A b s o l u t e and r e l a t i v e n a v i g a t i o n data s t o r e d i n t h i s d a y - f i l e were dumped onto magnetic tape t w i c e a day f o r a r c h i v i n g . The s h i p ' s d r i f t between s a t e l l i t e f i x e s was u n i f o r m l y d i s t r i b u t e d over the t r a c k i n t e g r a t e d by the EM-log. Program NAGUT c o r r e c t e d the n a v i g a t i o n data between s a t e l l i t e f i x e s .
4.3 Merging n a v i g a t i o n and CTD raw d a t a ( 1 s t p r o c e s s i n g )
The program f o r the f i r s t p r o c e s s i n g stage c a l l e d VMRAN formed a time b a s i s by e x t r a p o l a t i n g the s t a r t time of a CTD raw data b l o c k f o r t h e next 50 c y c l e s by i n t e g r a t i n g the sampling i n t e r v a l . I t searched f o r t h e matching 2-minute i n t e r v a l i n the n a v i g a t i o n f i l e s and i n t e r p o l a t e d the p o s i t i o n s l i n e a r l y . Thus f o r every 62.5 ms a c y c l e was c r e a t e d c o n t a i n i n g e x p l i c i t l y the time, the raw values from the CTD-sensors, the n a v i g a t i o n v a l u e s and the up/down f l a g .
4.4 C a l i b r a t i o n , e d i t i n g , data r e d u c t i o n , and c a l c u l a t i o n of d e r i v e d v a r i a b l e s (2nd p r o c e s s i n g )
I n order to minimize the number of output tapes c a l i b r a t i o n of CTD raw v a l u e s , e d i t i n g s p i k e s , data r e d u c t i o n and c a l c u l a t i o n of d e r i v e d v a l u e s were handled by one program c a l l e d MEDIT.
A time constant c o r r e c t i o n was a p p l i e d to the temperature v a l u e s i n o r d e r t o minimize the mismatch between the temperature and c o n d u c t i v i t y measure- ments. E m p i r i c a l t e s t s y i e l d e d a time constant of 85 ms needed to reduce
the s a l i n i t y spikes caused by t h i s mismatch. A d e s c r i p t i o n of these t e s t s i s given i n s e c t i o n 5.2. Then the raw values from the CTD sensors were transformed i n t o p h y s i c a l u n i t s u s i n g l a b o r a t o r y c a l i b r a t i o n c o e f f i c i e n t s i n a second order p o l y n o m i a l .
S a l i n i t y was c a l c u l a t e d from p r e s s u r e , temperature and c o n d u c t i v i t y and then f i l t e r e d w i t h a m e d i a n - f i l t e r (Sy, 1985) w i t h a 5-cyele window t o remove s p i k e s without e l i m i n a t i n g s t r o n g g r a d i e n t s . The data was then averaged over f i v e c y c l e s . The averaged temperatures and s a l i n i t i e s were used f o r the c a l c u l a t i o n of Oj- f o r each sensor p a i r r e s p e c t i v e l y .
4.5 P r e s s u r e monotonlsation and up-down s p l i t t i n g ( 3 r d p r o c e s s i n g )
Experience from former B a t f i s h experiments (GATE, Leach et a l . , 1985) showing s i g n i f i c a n t d i f f e r e n c e s i n the s i g n a l s of the ascending and descending p a r t s of the f i s h t r a c k which suggests s e p a r a t i n g them. As the f i s h d i d not f o l l o w e x a c t l y the c o n t r o l s i g n a l , the t u r n i n g p o i n t s had t o be determined from the d a t a . Program TURNP performed the f o l l o w i n g p r o c e s s i n g . The up/down-flag, which changed when the c o n t r o l s i g n a l switched from d i v e to c l i m b up or v i c e v e r s a , c o u l d be used as a c r i t e r i o n f o r s t a r t i n g the search f o r the next p r e s s u r e maximum or minimum w i t h i n a l i m i t e d number of c y c l e s . During the s e p a r a t i o n of ascents and descents, c y c l e s which were not monotonous i n p r e s s u r e were dropped. A p l a u s i b i l i t y check of the hydrographic data a l s o removed s i n g l e s e n s e l e s s v a l u e s caused by p a r i t y e r r o r s i n the raw data and s u b s t i t u t e d them by the p r e c e d i n g v a l u e .
The p r o f i l e s were counted and the number was s t o r e d as a l a b e l i n each d a t a c y c l e , even numbers f o r d e s c e n t s , odd numbers f o r a s c e n t s . Ascents and descents were s t o r e d i n separate f i l e s .
4.6 C a l i b r a t i o n c o r r e c t i o n of s a l i n i t y and pressure ( 4 t h p r o c e s s i n g )
The c a l i b r a t i o n of the c o n d u c t i v i t y sensors i n the l a b o r a t o r y was not s u f f i c i e n t l y e x a c t . The s a l i n i t i e s of the h o u r l y samples had t o be used f o r a c o r r e c t i o n of the c a l i b r a t i o n . The water sample s a l i n i t i e s were compared w i t h CTD s a l i n i t i e s i n space and time. Using a l i n e a r r e g r e s s i o n performed by program LINREG, c o r r e c t i o n parameters f o r a l i n e a r t r a n s f o r m a t i o n were c a l c u l a t e d ( f i g u r e 4.6.1). The c a l i b r a t i o n of p r e s s u r e a l s o had to be c o r r e c t e d . T h i s was achieved by u s i n g the d i s t r i b u t i o n of pressure at the upper t u r n i n g p o i n t ( f i g u r e 4.6.2). The p r e s s u r e values showed a temperature dependent negative o f f s e t AP(T).
p = P + AP(T)
rc o r r ">-\*-/
The pressure was c o r r e c t e d by adding the o f f s e t f o r the mean s u r f a c e temperature of a 4-hour f i l e . Using program EICH3 s a l i n i t y and p r e s s u r e were c o r r e c t e d and d e n s i t y was r e c a l c u l a t e d w i t h i n the new c a l i b r a t e d s a l i n i t i e s .
4.7 E l i m i n a t i o n of s m a l l d e n s i t y i n v e r s i o n s ( 5 t h p r o c e s s i n g )
At t h i s stage d e n s i t y was contaminated by i n v e r s i o n s due to s a l i n i t y s p i k e s which could not be removed by the preceding e d i t i n g methods. A median- f i l t e r w i t h a 5-cycle window on d e n s i t y was used to reduce as much of the s m a l l - s c a l e noise as p o s s i b l e . B i g g e r i n v e r s i o n s which were observed m a i n l y a t the bottom end of the p r o f i l e s were thought to be an a r t i f a c t of the s l o p e of the f i s h - t r a c k and t h e r e f o r e they should be e l i m i n a t e d i n the 6 t h p r o c e s s i n g . For c o n s i s t a n c y the s a l i n i t y was r e c a l c u l a t e d from temperature and the f i l t e r e d d e n s i t y . The f i l t e r i n g was done w i t h program MEDFIL and y i e l d e d the c l e a n data s e t , the b a s i s f o r v a r i o u s f u r t h e r a n a l y s i s .
4.8 Monotonisation and v e r t i c a l interpolation (6th p r o c e s s i n g )
For i s o p y c n i c a n a l y s i s the p r o f i l e s were monotonized i n d e n s i t y and i n t e r p o l a t e d on constant o^ - i n t e r v a l s of 0.025 kg m~3 w i t h program MONINT.
V e r t i c a l i n t e r p o l a t i o n onto constant pressure values was performed at i n t e r v a l s of 1.0 x 10 Pa. I s o p y c n a l or i s o b a r i c s u r f a c e s were e x t r a c t e d from the v e r t i c a l l y i n t e r p o l a t e d p r o f i l e s by appending and e x t r a c t i o n r o u t i n e s EDIT2 and EXTRAC.
the pressure d i f f e r e n c e s between a,, surfaces which were 0.1 kg m"3 a p a r t , w i t h i n the same r o u t i n e the depth of each i s o p y e n a l r e l a t i v e t o a chosen reference i s o p y e n a l was c a l c u l a t e d .
4.10 Objective analysis (8th p r o c e s s i n g )
The o b j e c t i v e a n a l y s i s method a p p l i e d to t h i s data s e t i s d e s c r i b e d i n Woods et a l . (1981). B r i e f l y , the method works as f o l l o w s : F i r s t l y the two- d i m e n s i o n a l a u t o - c o r r e l a t i o n f u n c t i o n (biased) of the data t o be a n a l y s e d was computed. A weighting f u n c t i o n ( f i g . 4.10) was d e r i v e d by smoothing t h i s raw a u t o - c o r r e l a t i o n f u n c t i o n , m u l t i p l y i n g i t by a c o n i c a l t a p e r and s e t t i n g negative values to zero. This w e i g h t i n g f u n c t i o n would reach a v a l u e of z e r o w i t h i n a f i n i t e number of g r i d l e n g t h s , n o r m a l l y l e s s t h a n e i g h t , depending on the c o r r e l a t i o n d i s t a n c e . The w e i g h t i n g f u n c t i o n was then used i n a s u c c e s s i v e - c o r r e c t i o n o b j e c t i v e a n a l y s i s scheme. I n o r d e r t o a v o i d i n f l u e n c i n g the r e s u l t s by s t a t i s t i c s w i t h d i f f e r e n t c h a r a c t e r i s t i c s the computation of the weighting f u n c t i o n c a r r i e d out s e p a r a t e l y f o r each parameter and each s u r f a c e . The a p p p l i e d program f o r o b j e c t i v e a n a l y s i s was c a l l e d OBANA.
D A T A P R O C E S S I N G F L O W D I A G R A M
r ' Processing
Merging Navigation d a t a with C T D - d a t a
'Raw C T D + Nav. d a t a \ a,?,A.,X,Y,RT1,T2,C1,C2,
2n d Processing
Calibration , Editing of S Data reduction. Derived variables
t.sc, A
<T1,T2,C1,C2,S1,
X , Y , P ^ \ i1,S2,fft1,Oj2y
3, d Processing
P-Monotonisation, U p - D o w n - Splitting, Plausibility Tests
Ascents^)
4, h Processing
Calibration correction of S and P 5t h Processing
Editing of S
R e c a l c u l a t i o n of S fromTand fft
Extraction of turning points Mixed layer determination Calculation of surface waterflux
i
(Sections)
"Clean data t,g>.A.,X,Y, P 1,T2,C1.C2,S1,S2,rjt1,0.
6'" Processing
Vertical interpolation on to standard s u r f a c e s
7'" Processing
Calculating vertical differences
2 :
r j P | g , . 4 T | gt, J S| o P 8, h Processing
Extraction of s u r f a c e s
<3T)p.4S|p.iflJp^
0 t - s u r f a c e P - s u r f a c e
; X.fX X,Y,P,T1,T2,S1,S2,ff,1-const.,ff|2 J A#,A.X.Y,P-const T1,T2,St.S2.Cf,1,fft2 ' à P|tfp*T|g,,éS\gt i T | p , i S | p , 4 0t| p
9" Processing
Objective analysis
Contoured maps on Gt surfaces
Contoured maps on P - s u r f a c e s
4.1: Flow diagram of t h e d a t a p r o c e s s i n g of the towed f i s h - CTD - d a t a . O v a l s c o n t a i n s t o r e d p r o c e s s i n g s t a g e s , r e c t a n g l e s a r e programs and rounded boxes i n d i c a t e standard p r o d u c t s .
34.5 35-0 35.5 C T . D - S a l i n i t y x 103
36.0
S a l i n i t y C a l i b r a t i o n f o r S e n s o r P a i r 2 NOA'81
36.0
35.5
35.0
a
£
J 34 5
3 4 5 3 5 0 35.5
C T 0 - S a l i m t y * 1 03
36.0
F i g . 4.6.1: Linear regression of s a l i n i t i e s of sailnametered water samples and raw calibrated CTD-data presented separately for each sensor p a i r . The slope and offset of the regression curve
the f i n a l calibration of CTD-sallnities.
F i g . 4.6.2: Sea s u r f a c e temperatures and d i s p l a y e d pressure v a l u e s where the f i s h reached the sea s u r f a c e . The t a n g e n t i a l l i n e was used t o c o r r e c t the temperature -dependent o f f s e t of the pressure gauge.
