Height above ground surface [m]Height above ground surface [m]

(1)

Mie Andreasen

Department of Geosciences and Natural Ressource Management University of Copenhagen

Majken C. Looms, Karsten H. Jensen, Heye Bogena,

Marek Zreda and Darin Desilets

(2)

TERENO International Conference 2014

Objective: To estimate intermediate scale biomass and canopy interception

Canopy interception:

‐ is the precipitation intercepted by the canopy of a tree/forest

‐ the interception loss can be important for the water balance

‐Skjern River catchment: 16% forest and approx. 200 rainy days per year.

Earlier studies estimate canopy interception loss to be around 40% of the total forest evaporation (Apr‐Oct 2010)

‐ is traditionally measured on a small scale (e.g. through‐fall stations) Biomass:

‐ detection is important given interests in bioenergy, climate change, wood production etc.

‐ is traditionally estimated through e.g. tree surveys, satellite/images retrievals

Through‐fall station

(3)

Cosmic‐ray transport

High energy particles Earth ´ s protecting forces:

‐the magnetic fields

‐the atmosphere (Moderation and absorption of the particles)

Inverse relationship between the cosmic‐ray neutron intensity and the hydrogen content (Unique ability of hydrogen to moderate neutrons)

Footprint

In the scale of hectometers in the air and decimeters in the ground

Hydrogen is pooled in the:

‐biomass

‐canopy interception

‐surface water

‐water vapour

‐soil moisture

‐soil organic compounds etc.

(4)

Method

Field equipment

Cosmic‐ray neutron probes:

‐ BARE probe; detects low‐energy neutrons

‐ MOD probe; detects high‐energy neutrons

Measurements

‐ multiple level measurements

‐ multiple neutron energy detection

‐ reference detection (above a water body)

Modeling, MCNPX

‐ an extended version of the Monte Carlo N‐Particle Transport Code

‐ a radiation transport code for simulating nuclear processes

(5)

Gludsted Plantation

Forest characteristics:

‐latitude: 56 ° N and 50 m abs.

‐flat terrain and sandy soils

‐a coniferous plantation

primarily Norway spruce; 20 and 40 years

‐forest area: approx. 3500 ha

‐biomass: approx. 100 t/ha above ground dry biomass (from Lidar images, 2006/2007)

‐thick litter layer (5‐7 cm)

(6)

Model conceptualization

‐ to setup a representative model

MCNPX model

‐ steady state model

Energy bins

‐ thermal neutrons; 0 ‐ 0.5 eV

‐ fast/epithermal neutrons; 0.5 ‐ 10

⁶

eV

A homogenous forest is simulated using average values for the forest and the soil:

‐ tree radius and height

‐ tree density

‐ forest biomass

‐ bulk density

‐ porosity

‐ carbon content etc.

Atmosphere

Forest layer

Litter layer Soil layer Forest layer seen

from above 

Forest layer seen

from the side 

(7)

Cosmic‐ray neutron intensity profiles

‐ Measurements vs. Model

Measurements:

Model:

1 1.5 2 2.5 3

x 10^‐10 0

5 10 15 20 25 30 35 40

Neutron intensity (relative)

Height above ground surface [m]

Thermal neutron intensity Tree trunk, Foliage, Air Point of measurement

3 3.5 4 4.5 5

x 10^‐10 0

5 10 15 20 25 30 35 40

Fast/epithermal neutron intensity Tree trunk, Foliage, Air Point of measurement

700 800 900 1000 1100

0 5 10 15 20 25 30 35 40

Neutron intensity [cts/hr]

Measurement point and standard deviation November 2013 March 2014 Canopy Surface

2000 300 400 500 600

5 10 15 20 25 30 35 40

Measurement point and standard deviation November 2013 March 2014 Canopy Surface

Mismatch between the measured and

modeled high‐energy

neutron intensity

(8)

Ringkøbing Fjord – Cadmium shield experiment

A cosmic‐ray neutron probe shielded by cadmium foil will detect neutrons with energies > 0.5 eV

Reference measurements

‐ conversion factor ‐ relative count rates (model) to actual count rates

> a chemical analysis of the fjord water is necessary!

25‐Mar‐2014200 26‐Mar‐2014

300 400 500 600 700 800

Cosmic-ray neutron intensity [counts/hr]

30‐Jun‐2014200 01‐Jul‐2014 02‐Jul‐2014 300

400 500 600 700 800

MOD neutron intensity Fast/epithermal neutron intensity BARE neutron intensity Thermal neutron intensity

0 1 2 3 4 5

‐10

0 5 10 15 20 25 30 35 40

Height above water surface [m]

Thermal neutron intensity Saltwater

Freshwater Point of measurement

0 1 2 3 4 5

‐10

0 5 10 15 20 25 30 35 40

Height above water surface [m]

Fast/Epithermal neutron intensity Saltwater

Freshwater Point of measurement

(9)

Cadmium shield experiments

– Correction factors

Correction factors for BARE and MOD probes has been calculated based on cadmium field experiment conducted at different:

‐ land covers

‐ heights above the ground surface

‐ soil types

(not included in the figure below)

(10)

A Cosmic‐ray neutron intensity profile (incl. a cadmium shielded MOD probe)

‐ Measurements (March 2013) vs. Model

Measurements:

Model:

The modeled

fast/epithermal neutron intensity is more in line with the measured cadmium shielded MOD neutron intensity

1 1.5 2 2.5 3

x 10^‐10 0

5 10 15 20 25 30 35 40

Thermal neutron intensity Tree trunk, Foliage, Air Point of measurement

3 3.5 4 4.5 5

x 10^‐10 0

5 10 15 20 25 30 35 40

Fast/epithermal neutron intensity Tree trunk, Foliage, Air Point of measurement

600 700 800 900

0 5 10 15 20 25 30 35 40

Measurement point & standard deviation, March 2014:

MOD+Cadmium MOD Canopy Surface

2000 300 400 500 600

5 10 15 20 25 30 35 40

Measurement point & standard deviation, March 2014:

BARE Canopy Surface

(11)

Model conceptualization

Tree trunk, Air

Foliage

Tree trunk, Foliage

Tree trunk, Foliage, Air

Wet canopy;

2 mm canopy interception

5 10 15 20 25 30 35 40

Thermal neutron intensity Dry canopy

Wet canopy Canopy surface Point of measurement

5 10 15 20 25 30 35 40

Fast/epithermal neutron intensity Dry canopy

Wet canopy Canopy surface Point of measurement

1 1.5 2 2.5 3

x 10^‐10 0

5 10 15 20 25 30 35 40

Thermal neutron intensity Tree trunk, Air Foliage Tree trunk, Foliage Tree trunk, Foliage, Air Canopy surface Point of measurement

3 3.5 4 4.5 5

x 10^‐10 0

5 10 15 20 25 30 35 40

Fast/epithermal neutron intensity Tree trunk, Air

Foliage Tree trunk, Foliage Tree trunk, Foliage, Air Canopy surface Point of measurement

(12)

A comparison of modeled and measured neutron intensities

‐ Preliminary

Actual counts rates:

a preliminary conversion factor derived from the boat experiment is used

Relative to ground surface values:

0.4 0.6 0.8 1

0 5 10 15 20 25 30 35 40

Model

Measurements, November 2013 Measurements, March 2014 Canopy surface

0.6 0.8 1 1.2 1.4

0 5 10 15 20 25 30 35 40

Model

1000 200 300 400 500 600 700

5 10 15 20 25 30 35 40

Model

3000 400 500 600 700 800 900

5 10 15 20 25 30 35 40

Model

(13)

Biomass modeling

‐ the effect of changing biomass and soil moisture

(14)