9. April 2023

Mit

glie

d d

er

Helm

holt

z-G

em

ein

sch

aft

Closed loop brightness temperature data inversion for the retrieval of soil hydraulic properties

Marin Dimitrov, Jan Vanderborght, K. Z. Jadoon, Lutz Weihermüller, Mike Schwank and Harry Vereecken

2011 International Geoscience and Remote Sensing Symposium (IGARSS)Vancouver, Canada

Soil Moisture Remote Sensing Session

9. April 2023 Folie 2IBG-3 Agrosphere

OutlineOutline

I. Introduction1. Motivation2. Measurement setup3. Measurement equipment

II. Measurement Results

1. Soil moisture 2. Soil temperature 3. Brightness temperature

III. Inverse modeling

1. Flow chart diagram 2. Results

IV. Conclusions

Radiometer JülBaRa with Radiometer JülBaRa with holding construction in the air.holding construction in the air.

Photo from July 2010Photo from July 2010

9. April 2023 Folie 3IBG-3 Agrosphere

MotivationMotivation

• Investigation of the soil surface structure effects on the spatio-temporal soil moisture and soil temperature distribution

• Estimation of the relationship between the surface soil moisture and temperature and the subsurface states

• Implementation of classical (in-situ) and remote sensing methods

9. April 2023 Folie 4IBG-3 Agrosphere

Measurement campaignMeasurement campaignGoalsGoals

5TE and SDI Sensors 5TE and SDI Sensors

Radiometer JülBaRa Radiometer JülBaRa

• Monitoring of the soil moisture and soil temperature of plots with different soil structure

• Characterization and calibration of the L-Band Radiometer JülBaRa

• Monitoring of the L-band brightness temperature over bare soil ploughed plot

• Linking of the L-Band brightness temperature with the soil hydraulic properties

9. April 2023 Folie 5IBG-3 Agrosphere

Measurement campaignMeasurement campaignMeasurement setupMeasurement setup

1

2 1

2

Measurements plotsMeasurements plots

Ploughed plot Ploughed plot

Seedbed plot Seedbed plot

Reference plot Reference plot

9. April 2023 Folie 6IBG-3 Agrosphere

Measurement campaignMeasurement campaignMeasurement equipmentMeasurement equipment

Used measurement equipment. Pictures from test field Selhausen.Used measurement equipment. Pictures from test field Selhausen.

9. April 2023 Folie 7IBG-3 Agrosphere

Technical Characteristics:

• L Band Radiometer (λ ≈ 21 cm, f ≈ 1.4 GHz)• 2 channels (1.4-1.414 and 1.415-1.43 GHz)• Dual polarized conical horn antenna

• -3 dB beamwidth of 12°

Measuring cycle and operation:

• Calibrations at TCold = 278 & THot = 338K• Full cycle lasts for 45 s• Measuring software Labview• Rotation at horizontal and vertical direction

• 0 – 140° in horizontal direction• 48 – 140° in vertical direction

L Band RadiometerL Band RadiometerJülBaRaJülBaRa

Holding construction and rotation Holding construction and rotation possibilities of JülBaRapossibilities of JülBaRa

JülBaRa is in permanent use since September 2009

9. April 2023 Folie 8IBG-3 Agrosphere

ResultsResultsSoil moistureSoil moisture

Meteorological data and measured soil moisture in 2, 5, 10 and 30 cm Meteorological data and measured soil moisture in 2, 5, 10 and 30 cm depth between 27.09.2009 and 27.10.2009depth between 27.09.2009 and 27.10.2009

9. April 2023 Folie 9IBG-3 Agrosphere

ResultsResultsBrightness temperatureBrightness temperature

Measured brightness temperature (horizontal and vertical polarization) at Measured brightness temperature (horizontal and vertical polarization) at 45° with L-Band Radiometer JülBaRa between 27.09.2009 and 27.10.200945° with L-Band Radiometer JülBaRa between 27.09.2009 and 27.10.2009

9. April 2023 Folie 10IBG-3 Agrosphere

ResultsResultsSoil temperatureSoil temperature

Measured soil surface temperature Measured soil surface temperature from 02.10 to 07.10.2009from 02.10 to 07.10.2009

Photo from 2 October 2009 (12 P.M.)Photo from 2 October 2009 (12 P.M.)Plot 3Plot 2

16.6 °C16.6 °C 16.3 °C16.3 °C

15.4 °C15.4 °C

Mean skin temperature for the plotsMean skin temperature for the plots

9. April 2023 Folie 11IBG-3 Agrosphere

ResultsResultsModeling procedureModeling procedure

Flow chart diagram of the inverse modeling procedureFlow chart diagram of the inverse modeling procedureInversion for the soil hydraulic parameters, fitting of the brightness temperature Inversion for the soil hydraulic parameters, fitting of the brightness temperature

Soil hydraulic parameters:θr, θs, α, n, Ks

Hydrological simulator Hydrus 1D

Meteorological data: Rain and ETo (from Tair, Solar, Wind and Humidity)

Simulated moisture

profile

Simulated permitivity (ε)

profile

Dielectric mixing model

ε

Simulated Reflectivity

pSIMR

Tb sim.

Inversion

Objective function: Φ=Σ(Tb sim.-Tb meas.)^2

RTM

Roughness correction

CRTM or Fresnel

Tb meas.

θ sim.

.corrpSIMR

Global optimization with SCE

Effective soil temperature

θ meas

9. April 2023 Folie 12IBG-3 Agrosphere

ResultsResultsModeling procedureModeling procedure

Θr [cm^3/cm^3]

Θs [cm^3/cm^3]

α [cm^-1]

n [-]

Ks [cm/min]

Unknown hydraulic parameters: θr, θs, Ks, n and α

MVGθr

cm3

/cm3

θs

cm3

/cm3

α

1/cm

n-

Ks

cm/day

l-

Laboratory 0.0 0.353 0.004 1.32 0.064 0.5

Inverted 0.03 0.42 0.001 1.60 0.030 0.5

Parameter development after 1500 iterations, using Fresnel

9. April 2023 Folie 13IBG-3 Agrosphere

ResultsResultsModeling procedureModeling procedure

Modeled and measured brightness temperature, modeled and Modeled and measured brightness temperature, modeled and measured soil moisturemeasured soil moisture

R^2 = 0.75

One to one line of the brightness temperatureOne to one line of the brightness temperature

9. April 2023 Folie 14IBG-3 Agrosphere

ConclusionsConclusions

• Measurement plots with different soil surface structures

• Measurement of various soil moisture and soil temperature values in the different plots

• strong (0.2 – 5.6° C) variation of the soil surface temperature at the beginning of the campaign

• lowest soil surface temperature in the reference plot

• lowest soil moisture in the ploughed plot

• highly comparable soil moisture values in the reference and the seedbed plot

9. April 2023 Folie 15IBG-3 Agrosphere

ConclusionsConclusions

• Complex coupled inversion procedure for estimation of soil hydraulic parameters

• Coupling of six different models and some additional calculations

• Multi objective task: comparison of modeled and measured brightness temperatures, further evaluation of the soil moisture

• Innovative method for handling radiometer data, assessment of the soil hydraulic parameters

• Implementation of the inversion procedure for the other plots

• Improvement of the inversion procedure is still needed

9. April 2023 Folie 16IBG-3 Agrosphere

AcknowledgmentsAcknowledgments

The authors thanks to:

• Assist. Prof. Kosta Kostov, Bulgarian Academy of Sciences for all of the consultations

• Francois Jonard, Dr. Jutta Bikowski, Christian Steenpass and Dr. Ulrike Rosenbaum

• Rainer Harms, Normen Hermes and Ferdinand Engels

• The whole ZAT team and IBG Workshop

The Research Unit MUSIS gratefully acknowledge the financial support from the

Deutsche Forschugsgemeinschaft.

9. April 2023 Folie 17IBG-3 Agrosphere

Thank you for your attention!

Radiometer field of view from above, July 2010 Radiometer field of view from above, July 2010