Role of Soil Moisture/Climate Networks in SMAP Validation

T. J. JacksonUSDA ARS Hydrology and Remote Sensing Lab

Beltsville, MDDec. 4, 2008

Outline

• Remote sensing of soil moisture

• SMAP Overview

• SMAP Cal/Val plan

• Experiences with AMSR-E

• Some things that must be addressed

Remote Sensing of Soil Moisture

• Soil moisture information derives from changes in the dielectric properties resulting from changes in water content.

• Freeze-thaw information derives from changes in the dielectric properties resulting from temperature changes

• Progress has been limited by the available sensors: sensitivity and spatial resolution.

• So far there have not been any missions designed for soil moisture.

Sensitivity: Lower Frequencies Provide Information on a Deeper Soil Layer and are

Less Affected by the Vegetation

1 2 3 5 10 20 30 50Low

High

Frequency (GHz)

Sen

siti

vity

Bare

AquaAqua Meteorological Meteorological Satellites Satellites

Vegetated

1970s20022009-2013• Sensitivity of brightness temperature to changes in soil moisture

• An optimal system maximizes sensitivity for both bare and vegetated surfaces

• L-band: 1.4 GHz or 21 cm

SMOS SMOS Aquarius Aquarius SMAPSMAP

• Lower frequency means deeper soil sensing and less vegetation interference.

• It also means coarser spatial resolution using conventional antenna technology.

• Spatial resolution restricts potential applications.• The challenge is to achieve better sensing with higher spatial

resolution.• SMOS will explore a potential technology but will provide

only a 40 km resolution.• SMAP will explore a potential technology and different

instrument design and will provide a 10 km resolution.

Spatial Resolution: Overcoming Passive Microwave Limitations

100 km 10 km 1 km

Day

Week

Month ALOS SAR

Aquarius

SMOS SMAP Radar-Radiometer

ClimateClimate ApplicationsApplications

Weather ApplicationsWeather Applications

CarbonCarbon CycleCycle ApplicationsApplications

Resolved Spatial Scales

Res

olve

d T

emp

oral

Sca

les

Radio

met

er

RadarEvolution of L-Band Sensing

Evolution of L-Band Remote Sensing (Land)

*Material from SMAP Science Team

• Lower frequency means deeper soil sensing and less vegetation interference.

• It also means coarser spatial resolution using conventional antenna technology.

• Spatial resolution restricts potential applications.• The challenge is to achieve better sensing with higher spatial

resolution.• SMOS will explore a potential technology but will provide

only a 40 km resolution.• SMAP will explore a potential technology and different

instrument design and will provide a 10 km resolution.

Spatial Resolution: Overcoming Passive Microwave Limitations

Soil Moisture Active Passive (SMAP) Satellite

Soil Moisture Active Passive Mission (SMAP)

• NASA• One of the first missions resulting from the NRC Decadal

Survey• Soil moisture and freeze-thaw• Three day global coverage• Launch 2013

SMAP Mission Concept• L-band radar and radiometer

system with 6-m reflector• Solution to spatial resolution is

two-fold; a technology that uses a large antenna (deployable mesh) and enhanced resolution by combining high accuracy radiometry retrieval with high resolution radar. Soil moisture products;– Radar resolution: 3 km– Radiometer resolution: 40 km– Combined product: 10 km

SMAP Status• SMAP Project and Program (March 2008)• Key Project Personnel

– Program Executive: E. Ianson (NASA/Hq)– Program Scientist: J. Entin (NASA/Hq)– Project Manager: K. Kellogg (JPL)– Project Scientist: E. Njoku (JPL)– Deputy Project Scientist: P. O'Neill (GSFC)

• Science Definition Team (SDT) (Selected Oct. 2008)– D. Entekhabi, MIT, Team Leader– W. Crow, U.S. Department of Agriculture– T. Jackson, U.S. Department of Agriculture (Validation WG)– J. Johnson, Ohio State University (RFI WG)– J. Kimball, University of Montana– R. Koster, NASA Goddard Space Flight Center– K. McDonald, Jet Propulsion Laboratory– M. Moghaddam, University of Michigan (Algorithm WG)– S. Moran, U.S. Department of Agriculture (Applications WG)– R. Reichle, NASA Goddard Space Flight Center– J. Shi, University of California, Santa Barbara– L. Tsang, University of Washington– J. van Zyl, Jet Propulsion Laboratory

• SRR/MDR/PNAR Review (February 2009)• Algorithm and C/V Workshop (June 2009)• Applications Workshop (September 2009)

SMAP Validation

• Based on SMAP mission requirements and mission product ATBDs

• Objectives: – Demonstrate that the science requirements have

been met post-launch and over the mission life – Improve soil moisture and freeze-thaw algorithms

and products– Demonstrate the impact or value of mission products

on specific applications

SMAP L1 Requirements Traceability

Science Objectives

Scientific Measurement Requirements

Instrument Functional Requirements Mission Functional Requirements

Soil Moisture: 4% volumetric accuracy in top 5 cm for vegetation water content < 5 kg m-2; Hydrometeorology at 10 km; Hydroclimatology at 40 km

L-Band Radiometer: Polarization: V, H, U; Resolution: 40 km; Relative accuracy*: 1.5 K L-Band Radar: Polarization: VV, HH, HV; Resolution: 10 km; Relative accuracy*: 0.5 dB for VV and HH Constant incidence angle** between 35° and 50°

Freeze/Thaw State: Capture freeze/thaw state transitions in integrated vegetation-soil continuum with two-day precision, at the spatial scale of landscape variability (3 km).

L-Band Radar: Polarization: HH; Resolution: 3 km; Relative accuracy*: 0.7 dB (1 dB per channel if 2 channels are used); Constant incidence angle** between 35° and 50°

DAAC data archiving and distribution. Field validation program. Integration of data products into multisource land data assimilation.

Sample diurnal cycle at consistent time of day Global, 3-4 day revisit; Boreal, 2 day revisit

Swath Width: 1000 km Minimize Faraday rotation (degradation factor at L-band)

Orbit: 670 km, circular, polar, sun-synchronous, ~6am/pm equator crossing

Understand processes that link the terrestrial water, energy and carbon cycles; Estimate global water and energy fluxes at the land surface Quantify net carbon flux in boreal landscapes Enhance weather and climate forecast skill Develop improved flood prediction and drought monitoring capability.

Observation over a minimum of three annual cycles

Minimum three-year mission life Three year baseline mission***

* Includes precision and calibration stability ** Defined without regard to local topographic variation *** Includes allowance for up to 30 days post-launch observatory check-out

SMAP Science Data Products

Data Product Description

L1B_S0_LoRes Low Resolution Radar so in Time Order

L1C_S0_HiRes High Resolution Radar so on Earth Grid

L1B_TB Radiometer TB in Time Order

L1C_TB Radiometer TB on Earth Grid

L3_SM_HiRes_3km Radar Soil Moisture on Earth Grid

L3_SM_40km Radiometer Soil Moisture on Earth Grid

L3_SM_A/P_10kmRadar/Radiometer Soil Moisture on Earth Grid

L3_F/T_HiRes Freeze/Thaw State on Earth Grid

L4_SMSoil Moisture Model Assimilation on Earth Grid

L4_F/TFreeze/Thaw Model Assimilation on Earth Grid

ATBDs under development.

Surface 0-5 cm

Profile

}

Demonstrate that the science requirements have been met post-

launch and over the mission life• Approach

– Provide verified estimates of soil moisture over an area and depth equivalent to that measured by the SMAP radiometer and radar instruments or derived products throughout the project life

– Provide a robust set of cover conditions and geographic/climate domains for validation

– Provide continuous, consistent, and long term records with minimal latency

• Elements: – Ground based soil moisture observations that represent

footprint/grid soil moisture either by replication or scaling, which has been verified

– Field experiments– Satellite product comparisons– Model product comparisons

SMAP Science Data Products

Data Product Description

Validation

NetworksField Exp.

Satellite Products

Model Product

s

L1B_S0_LoRes Low Resolution Radar o in Time Order x Aquarius

L1C_S0_HiRes High Resolution Radar o on Earth Grid x PALSAR

L1B_TB Radiometer TB in Time Order xSMOS

Aquarius

L1C_TB Radiometer TB on Earth Grid SMOS

L3_SM_HiRes_3km

Radar Soil Moisture on Earth Grid x x

L3_SM_40km Radiometer Soil Moisture on Earth Grid x xSMOSGCOM-

Wx

L3_SM_A/P_10kmRadar/Radiometer Soil Moisture on Earth Grid

x x x

L3_F/T_HiRes Freeze/Thaw State on Earth Grid TBD TBD TBD

L4_SMSoil Moisture Model Assimilation on Earth Grid

x SMOS x

L4_F/TFreeze/Thaw Model Assimilation on Earth Grid

TBD x

In Situ Soil Moisture

• Core element of validation-challenging problems– A single point within a satellite footprint is not

going to provide a reliable estimate of the spatial average.

• Robust validation requires international cooperation

• AMSR-E experiences

USA Oklahoma Networks Little Washita

Australia New South Wales Networks Kyeemba

Global In Situ Soil Moisture Validation Resources

• Coverage gaps: some are real, others are the due to communication or cooperation

• There are issues that need to be addressed if these are to be of value to validation.– Continuity

– Calibration

– Replication

– Scaling

– Coverage gaps

– Infrastructure

• There are a substantial number of in situ resources available for validation. Only a few provide the right kind of data (depth, frequency, latency, access)

• Some regions (OK and NSW) have exceptional resources.

In Situ Soil Moisture

• Core element of validation-challenging problems– A single point within a satellite footprint is not

going to provide a reliable estimate of the spatial average.

• Robust validation requires international cooperation

• AMSR-E experiences

Standards

Infrastructure

Diverse Conditions

Replication

Installation

Calibration

Scaling

Archive

Algorithm Validation

SMEX+

Validation of AMSR-E Soil Moisture Products

Using Watershed Networks

Lessons Learned

Little Washita Vitel Network

Berg

111

NOAA

136

144146

159162

154

133134

149151

5 cm

3-7 cm

Little Washita River Washita

Berg

111

NOAA

136

144146

159162

154

133134

149151

5 cm

3-7 cm

Little Washita River Washita

Little Washita, OK

Little River, GA

Walnut Gulch, AZ

Reynolds Creek, ID

AMSR-E U.S. Soil Moisture Validation Sites

-110 .25 -110 .15 -110 .05 -109 .95 -109 .8531 .50

31 .60

31 .70

31 .80

31 .90

-117.00 -116.90 -116.80 -116.70 -116.6042.95

43.05

43.15

43.25

43.35

-83.90 -83.80 -83.70 -83.60 -83.5031.40

31.50

31.60

31.70

31.80

-98 .30 -98.20 -98.10 -98.00 -97.9034.65

34.75

34.85

34.95

35.05

a) L ittle W ash ita , O K b) L ittle R iver, G A

d) R eyno lds C reek , IDc) W alnu t G u lch , A Z

Longitude W (Degrees)

Latit

ude

N (

Deg

rees

)

+ R ain gage E x isting S M site

+ R ain gage E x isting S M S ite

+ R ain gage E x isting S M S ite

+ R ain gage E x isting S M S ite+ +

+ +

Standards

Infrastructure

Diverse Conditions

Replication

Installation

Calibration

Scaling

Archive

Algorithm Validation

SMEX+

Validation of AMSR-E Soil Moisture Products

Using Watershed Networks

Lessons Learned

Algorithm Comparison

• Three algorithms• 5 years of data

Algorithm Validation-Summary

Reynolds Creek, ID (Asc)

0

0.1

0.2

0.3

0.4

0.5

0 0.1 0.2 0.3 0.4 0.5Observed Soil Moisture (m3/m3)

Esti

mate

d S

oil

Mo

istu

re (

m3/m

3)

A

B

C

Little River, GA (Asc)

0

0.1

0.2

0.3

0.4

0.5

0 0.1 0.2 0.3 0.4 0.5Observed Soil Moisture (m3/m3)

Esti

mate

d S

oil

Mo

istu

re (

m3/m

3)

A

B

C

Little Washita, OK (Asc)

0

0.1

0.2

0.3

0.4

0.5

0 0.1 0.2 0.3 0.4 0.5Observed Soil Moisture (m3/m3)

Esti

mate

d S

oil

Mo

istu

re (

m3/m

3)

A

B

C

Walnut Gulch, AZ (Asc)

0

0.1

0.2

0.3

0.4

0.5

0 0.1 0.2 0.3 0.4 0.5Observed Soil Moisture (m3/m3)

Esti

mate

d S

oil

Mo

istu

re (

m3/m

3)

A

B

C

SMAP Soil Moisture Validation: In Situ Resources

• Ground based networks are a core component: provide actual quantitative soil moisture observations to evaluate algorithm performance– Continue/establish a number of dedicated soil

moisture validation sites

– Develop techniques for scaling sparse networks to footprints

– International cooperation

– Access and archiving

– Similar issues with freeze-thaw (temperature) and profile SM