Soil moisture retrieval using ALOS PALSAR

T. J. Jackson, R. Bindlish and M. CoshUSDA ARS Hydrology and Remote Sensing Lab, Beltsville, MD

J. ShiUniversity of California Santa Barbara, CA

November 6, 2008

Project Background • Radar remote sensing provides very high

spatial resolution data that can be used to estimate soil moisture.

• Robust retrieval methods have not been developed.

• Limitations of previous satellites systems have been the wavelength and the number of independent radar parameters.

• ALOS PALSAR includes a low frequency and multiple polarizations that may lead to improved soil moisture retrievals.

• Scaling from PALSAR to SMAP

Outline• Soil Moisture Active Passive (SMAP) Mission

– Mission description– Role of PALSAR

• Cloud Land Surface Interaction Campaign (CLASIC)– PALS/PALSAR– Soil moisture retrieval

• SMAP Validation Experiment 2008 (SMAPVEX08)

Soil Moisture Active Passive (SMAP) Satellite

Soil Moisture Active Passive Mission (SMAP)

• NASA• One of the first missions

resulting from the NRC Decadal Survey

• L-band: microwave radar (1-3 km), microwave radiometer (40 km)– 40 degrees incidence angle– Polarimetric

• Three day global coverage

• Launch 2013

SMAP Mission Concept• Radiometers and radars each have

advantages and disadvantages for soil moisture. – Limited spatial resolution of the radiometer

and the robustness of the radar algorithms

• SMAP will attempt to overcome these with:– A technology that provides a large aperture

low mass/volume antenna (deployable mesh) – Enhanced resolution by combining high

accuracy radiometer retrieval with high resolution radar (10 km product)

SMAP Science and Applications

1. Ecosystem Response (Variability and Change)2. Agricultural and Ecosystem Productivity3. Wild-Fires4. Mineral Dust Production

Land-Use, Ecosystems, and Biodiversity

1. Heat Stress and Drought2. Vector-Borne and Water-Borne Infectious DiseaseHuman Health and Security

1. Longer-Term and More Reliable Atmospheric ForecastsClimate / Weather

1. Floods and Drought Forecasts2. Available Water Resources Assessment3. Link Terrestrial Water, Energy and Carbon Cycles

Water Resources and Hydrological Cycle

Cited SMAP ApplicationsDecadal Survey Panels

• Societal benefit and applications will impact mission development and implementation

• Applications that utilize SMAP (and SMOS) observations will be of great interest to NASA and supported under a variety of programs

*Material from SMAP Science Team

SMAP Status

• NRC Decadal Survey Report (Jan. 2007)• NASA prioritization (Feb. 2008)• SMAP Project and Program (March 2008)• Science Team Selected (October 2008)• Launch 2013

SMAP Synergy With Other Missions/Applications

• A great decade for low frequency microwave remote sensing!• SMAP provides continuity for L-band measurements of

ALOS, SMOS, and Aquarius, and synergy with GPM and GCOM-W

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SMAPGPM

GCOM-WAquarius

SMOSALOS

Estimated Mission Timeline

*Material from SMAP Science Team

100 km 10 km 1 km

Day

Week

Month ALOSSAR

Aquarius

SMOS SMAP Radar-Radiometer

ClimateClimate ApplicationsApplications

Weather ApplicationsWeather Applications

CarbonCarbon CycleCycleApplicationsApplications

Resolved Spatial Scales

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olve

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cale

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RadarEvolution of L-Band Sensing

Evolution of L-Band Remote Sensing

*Material from SMAP Science Team

Relevant Issues (PALSAR/SMAP)• RFI information for design• Data resource for algorithm design and

validation. – How do high resolution SAR data (PALSAR)

scale to 1-3 km (SMAP)? Can we use PALSAR to simulate SMAP radar?

• Field experiments with SMAP simulator and concurrent PALSAR coverage. (challenge)– CLASIC– SMAPVEX08

CLASIC • June 2007 Southern Great Plains

Oklahoma (included the LW)• Intensive ground sampling of soil

moisture over a one month period • Aircraft coverage with the Passive Active

L-band System (PALS) (SMAP Simulator)

Single beam

Fixed angle (40 degrees)

Spatial resolutions ~ 0.3(Altitude)

First deployment of new antenna

PALS Experiment Design over the Little Washita Watershed

• 8 lines in east-west direction

• Spatial resolution ~400 m

• 11 flights• Predominantly

pasture and dry winter wheat

9ALOS FS

8LW

76FC, LW

543

1615141312FC, LW

11LW

10FS

23FC

22212019FC, LW

1817

302928272625FC

24FC, CF

7LW

6FC, LW

5FC, LW

4LW

3FC, LW

21FC, LW ALOS LW

CLASIC Radar Coverage June-July 2007

Legend: Blue=PALS, Green=ALOS and PALS

PALS Radiometer Mapping• L-band H-polarization over Little Washita Watershed

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Brightness Temperature (K)

PALS Radiometer and Radar Mapping• L-band H-polarization and HH over Little Washita Watershed

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Backscatter Coefficient

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PALSAR FBD– Little Washita July 1, 2007

hh=r,b hv=g70 kmSwath

34.3 deg

Incidence Angle

HH+HV

Polarization

14 MHz

Bandwidth

Comparison Between PALS and PALSAR• Cross-validation of radars and

scaling.• Averaged PALSAR observations for

every PALS footprint (400 m resolution).

• Note that– Backscatter coefficient decreases with

decrease in incidence angle - PALSAR measurements should be slightly smaller than PALS.

– The two sensors also have different azimuth angles.

Comparison Between PALS and PALSAR• Cross-validation of radars and

scaling.• Averaged PALSAR observations for

every PALS footprint (400 m resolution).

• Note that– Backscatter coefficient decreases with

decrease in incidence angle - PALSAR measurements should be slightly smaller than PALS.

– The two sensors also have different azimuth angles.

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PALSAR Sigma0

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HH (SEE=1.80)

HV (SEE=1.91)

• Some of the scatter can be attributed to the sub-pixel variability and noise. Resolution : PALSAR (12.5 m), PALS (400 m).

• Good agreement between the two sensors without significant bias indicates comparative calibration and possibly linear scaling.

Soil Moisture Retrieval-Preliminary

• Next phase will retrieve soil moisture from the radiometer and radar of PALS and PALSAR.

• Current approach employs the Dubois Model, however, – There is no vegetation parameterization– Requires hh and vv – can be directly applied to

PALS data– For PALSAR an adaptation for using hv instead of

vv is needed

SMAP Validation Experiment 2008(SMAPVEX08)

• Support for SMAP science issues• Primary study area will be the Delmarva

peninsula (Choptank Watershed).• Multiple flights over a two week period (Sept.

29-Oct. 13, 2008)• Two aircraft; four sensors• Spatial resolutions of 1 and 3 km (more typical

of SMAP than in CLASIC)

SMAPVEX08 Choptank Site

100 km

SMAP Validation Experiment 2008(SMAPVEX08)

• Support for SMAP science issues• Primary study area will be the Delmarva

peninsula (Choptank Watershed). • Multiple flights over a two week period (Sept.

29-Oct. 13, 2008)• Two aircraft; four sensors• Spatial resolutions of 1 and 3 km (more typical

of SMAP than in CLASIC)

Sensors and Platforms• PALS – Twin Otter

– L-band, fully polarimetric radar/radiometer– 40 degrees backward looking– Spatial resolution ~ 0.3(Altitude): selected altitude will yield a ground resolution of ~1000 m– Payload will include alternative RFI mitigation

• GSFC Digital Beam-forming Radar on P-3– L-band, fully polarimetric– +/- 45 degrees cross track– Altitudes (40 degree spatial resolution); 2000 m (1600 m) 5000 m (4200 m)

• Comrad – Ground Based– L-band, fully polarimetric radar/radiometer– Multiple angles– Spatial resolution ~ 50 m

• MAPIR Radiometer on P-3– L-band passive microwave– 40 degrees conically scanned– Altitudes (Spatial resolution); 2000 m (1000 m) 5000 m (2200 m)

• PALSAR – ALOS– L-band FBD HH, HV– 34.3 degrees– Sparial resolution of 12.5 m– Limited dates … Oct. 8

SMAPVEX08

PALS and COMRAD

Sensors and Platforms• PALS – Twin Otter

– L-band, fully polarimetric radar/radiometer– 40 degrees backward looking– Spatial resolution ~ 0.3(Altitude): selected altitude will yield a ground resolution of ~1000 m– Payload will include alternative RFI mitigation

• GSFC Digital Beam-forming Radar on P-3– L-band, fully polarimetric– +/- 45 degrees cross track– Altitudes (40 degree spatial resolution); 2000 m (1600 m) 5000 m (4200 m)

• Comrad – Ground Based– L-band, fully polarimetric radar/radiometer– Multiple angles– Spatial resolution ~ 50 m

• MAPIR Radiometer on P-3– L-band passive microwave– 40 degrees conically scanned– Altitudes (Spatial resolution); 2000 m (1000 m) 5000 m (2200 m)

• PALSAR – ALOS– L-band FBD HH, HV– 34.3 degrees– Sparial resolution of 12.5 m– Limited dates … Oct. 8

PALSAR 34.3o

Radar Scaling (RSCALE) Design

P3 Line

TO Line

Portion of July 8, 2008 PALSAR IMAGE

PALS 40o

1 km

Twin Otter Line

DBSAR 40o

3 km

• Establish the scaling of PALSAR (12.5 m) to SMAP radar resolution via high altitude PALS (1 km)

• Establish the scaling of PALSAR (12.5 m) to SMAP radar resolution via high altitude DBSAR (3 km)

• Establish the scaling of PALS (1 km) to DBSAR (3 km) radar resolution

May 23, 2008

July 8, 2008

Aug 23, 2008

PALSAR FBD Coverage of the Choptank Site

hh=r,b hv=g

PALSAR FBD Coverage of the Choptank Site

• October 8 data acquisition was cancelled due to a re-tasking a few days before. Our request was the default mode for this cycle.

• No “disaster” we could identify.• We only found out by checking acquisition

planning schedule … never contacted.• Asked for a reversal…...• There is a need for improvement in the

communications and prioritization.• Future plans.

SMAP Major Field Campaignsver. 10/08

SMAPVEX082008

2015

SMAPVEX142014

SMAPVEX13SMAP2013

GCOM-W2012

SMAPVEX112011

EuropeSMAPVEX10

AquariusAustralia

SMAPVEX10Australia

2010

AustraliaAustraliaEurope/Canada

SMOS2009

4321Year/Quarter

• SMAPVEX08– High priority design/algorithm issues

• Australia 2009-2010– 4 one-week campaigns to span four

seasons– Aircraft Radar/Radiometer– Separate SMOS validation

• Europe 2009-2010 (and Canada)– SMOS validation…launch delays

possible– No radar

• SMAPVEX10:CLASIC– Spring-Summer 2010– Oklahoma– SMOS and Aquarius available– Focus of algorithm validation

• SMAPVEX11– Focus on different problems; FT,

regions, seasons• SMAPVEX13 and 14

– SMAP product validationSatellite Launch in Red