0 10 20 30 OH VMR [ppbv]
15 20 25 30 35
Altitude [km]
THz 10318 THz 16295 TELIS observation; 24 January 2010
Figure 6.34: OH profiles retrieved from the TELIS balloon flight data on 24 January 2010. The solid red and green lines correspond to the OH profiles obtained from measurements 10318 and 16295, respectively. The dashed lines refer to the overall accuracy of both OH profiles.
consistent with the sensitivity analysis regarding the identical transition triplet in Sect. 5.2.1.
In the case of the second OH microwindow, all error components excepting the temperature error, are smaller than 1.5–2 ppbv below 30 km. The model parameter errors due to spectroscopy and calibration stretch from 25 km upwards where OH abundances start to increase. Above 30 km, however, all errors steeply increase.
The most obvious difference between the error budgets estimated for the two OH microwin-dows is reflected by the contribution of the spectroscopic parameter and calibration errors. For example, the spectroscopy error seems to have a significant contribution above 20 km in the case of the second microwindow. This is mainly due to the strength of the OH triplet and the interfering effect from the O3 line.
For the first time, OH retrievals from TELIS measurements are presented. Because of the large measurement noise, the precision in the OH retrievals is not highly satisfactory. Unfortu-nately, there is no other instrument measuring the same transitions of OH as TELIS, and only a few far infrared observations are available. The MLS instrument has not been measuring OH regularly, because the THz module on MLS has been in standby mode most of the time after 2009, and a limited number of measurements have been acquired since 2011. Another option is to compare the retrieved profiles with ground-based measurements and sophisticated chemical models. Further investigations into cross-validations of the TELIS OH profiles are ongoing.
4 4.1 4.2 4.3 4.4 4.5 f
IF [GHz]
-4 -2 0 2 4
Rel. diff. [%]
1.3e-13 1.4e-13
Radiance [W / (m2 sr Hz)]
measured fitted
fLO = 1842.2862 GHz; tangent: 18 km
(a)
4 4.1 4.2 4.3 4.4 4.5
fIF [GHz]
-6 -4 -2 0 2 4 6
Rel. diff. [%]
5e-14 6e-14 7e-14
Radiance [W / (m2 sr Hz)]
measured fitted
fLO = 1842.2862 GHz; tangent: 22 km
(b)
4 4.1 4.2 4.3 4.4 4.5
fIF [GHz]
-30 -15 0 15 30
Rel. diff. [%]
0 1e-14 2e-14 3e-14 4e-14
Radiance [W / (m2 sr Hz]
measured fitted
fLO = 1842.2862 GHz; tangent: 26 km
(c)
4 4.1 4.2 4.3 4.4 4.5
f
IF [GHz]
-40 -20 0 20 40
Rel. diff. [%]
-1e-14 0 1e-14 2e-14
Radiance [W / (m2 sr Hz)]
measured fitted
f
LO = 1842.2862 GHz; tangent: 30 km
(d)
Figure 6.35: Comparison of measured and modelled TELIS OH spectra in frequency segment 1 of the second OH microwindow during the 2010 flight. The spectra are plotted for tangent heights of (a)18, (b)22,(c)26, and(d)30 km. The dedicated measurement identifier is 16295.
-0.2 0 0.2 0.4 0.6 0.8 1 1.2
Averaging kernel 10
15 20 25 30 35
Altitude [km]
TELIS 10890; 11 March 2009
(a)
-0.2 0 0.2 0.4 0.6 0.8 1 1.2
Averaging kernel 15
20 25 30 35
Altitude [km]
TELIS 16295; 24 January 2010
(b)
Figure 6.36: Averaging kernels for the OH retrievals from TELIS far infrared measurements(a)10890 and(b)16295, respectively.
0 2 4 6 OH error [ppbv]
10 15 20 25 30 35
Altitude [km]
smoothing
measurement noise spectroscopy calibration sideband ratio pointing temperature pressure RSS_total
Figure 6.37: Smoothing, noise, and model parameters errors for the OH retrieval in the first microwin-dow. The estimates correspond to TELIS’s far infrared measurement 10890 during the 2009 flight.
0 2 4 6
OH error [ppbv]
15 20 25 30 35
Altitude [km]
smoothing
measurement noise spectroscopy calibration sideband ratio pointing temperature pressure RSS_total
Figure 6.38: Smoothing, noise, and model parameters errors for the OH retrieval in the second mi-crowindow. The estimates correspond to TELIS’s far infrared measurement 16295 during the 2010 flight.
performed. The conclusions of our analysis can be summarized as follows:
• O3 has been first retrieved by looking into different microwindows containing diverse O3 signatures. The inversion results obtained in different frequency segments of the same microwindow demonstrate that from a spectroscopic point of view, a consolidated O3
retrieval is attained by considering not only the pronounced transitions with less inter-fering contributions from other molecules, but also by selecting that transitions with low sensitivity to the temperature accuracy. Although the TELIS profiles are somewhat over-estimated around 23 and 30 km as compared to the MIPAS-B profiles, the shape of both profiles are overall consistent.
Two sets of comparisons of TELIS profiles against three spaceborne O3 profiles have been discussed. The first comparison indicates that the TELIS O3product is rather comparable with the profiles obtained by SMILES, whereas some discrepancies between the TELIS and MLS profiles between 25 and 28 km show up. In spite of the fact that the chosen SMR ozone data shows some oscillations due to a weaker regularization, the TELIS and SMR profiles for the second comparison agree well.
• HCl observations have been performed from the flight data on 24 January 2010 inside the activated Arctic vortex; these data were utilized for several internal and external comparisons. The absence of HCl was observed at about 23 km, which is consistent with the retrieval results provided by the TELIS submillimeter spectra and other spaceborne observations.
Compared to the HCl profiles retrieved from the 625.0 and 625.9 GHz transitions by SRON, the profile retrieved from the 1873.40 GHz transition resembles (almost) the same structure in the stratosphere, albeit with a bit higher concentration above 30 km. One of the main differences between the error characterizations of the two channels arise from the different transition lines in the corresponding ranges. Also, the two TELIS-THz HCl profiles have been compared with the coincident spaceborne observations performed by SMILES and MLS for the local noon measurements on 24 January 2010.
The simultaneous fitting of a combination of far infrared and submillimeter spectra demon-strates a successful attempt on exploiting more useful information from extended frequency ranges. This result has been proven by the improved averaging kernels, particularly at lower altitudes.
• CO observations have been presented for the 2010 and 2011 balloon flights. In 2010, three CO measurements have been analyzed and the concentration amount below 30 km has been found to be very small. The peak at 32.5 km is captured by all three profiles. Only one CO profile retrieved from the 2011 flight data was useful, and the peak value occurs at 26.5 km. The other measurement was not used for the retrieval as it was recorded when the balloon was unstable. The 2010 CO data are selected for comparisons against MLS observations and both agree very well over the considered altitude range.
• First OH retrievals have been performed for the measurements recorded during the 2009 and 2010 flights. We have retrieved the profiles for both OH transition triplets and found that the transition around 1837.80 GHz offers a higher sensitivity. The concentration changed gradually for the 2009 retrievals, especially below 25 km. The retrieval error is estimated to be large above 30 km due to the limited information.
• For all these retrievals, the most important model parameter errors at lower altitudes are the pointing and pressure profile, while the errors in the radiometric calibration and spectroscopic parameters are dominant in the middle stratosphere (above 25 km) where the concentration of the target species is high. Among possible error sources for the 1.8 THz channel, the measurement noise appears to be a severe issue despite the fact
that the noise errors are not discernible in the 480–650 GHz channel (e.g. approximately 0.01 ppbv for HCl). The smoothing error, in most cases, only affects the retrieval below 20 km since the useful information is limited. In fact, the retrieval performance can still be improved by a better characterization of the instrument, since the current overall accuracy is dominated by the measurement noise and instrument model parameter errors. In most cases (excepting OH), the associated measurement response is 0.8 over the altitude range from about 20 km up to the observer altitude.
These results have demonstrated TELIS’s high capability of observing atmospheric minor constituents in the middle atmosphere, i.e. lower and middle stratosphere, and through the comparisons with other limb sounders the retrieval program PILS proves to deliver reliable products from the TELIS data.