High-Resolution Enhanced Product Based on SMAP Active-Passive Approach using

Sentinel 1A and 1B SAR Data

Narendra N. Das1, Dara Entekhabi2, Seungbum Kim1, Scott Dunbar1, Andreas Colliander1

Simon Yueh1, Thomas Jagdhuber3, Jeff Walker4

1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA 2 Massachusetts Institute of Technology, Cambridge, MA, USA

3German Aerospace Center, Microwaves and Radar Institute, Oberpfaffenhofen, Germany4Monash University, Australia

a) Introduction to the SMAP Active-Passive (AP) Algorithm and potential to use Sentinel SAR

b) Sample of SMAP_Sentinel Active-Passive Product

c) AP Algorithm Parameters Estimation

d) Validation of the Algorithm Output Using the Airborne Data from SMAPEx

e) Validation of the High Resolution Soil Moisture Product Using the Data from the SMAP Cal/Val Core Sites

f) Conclusion

Outline of the Presentation

SMAP AP Algorithm Adaptation

Heritage

Requires change due to following developments:

a) Estimate new parameters for C-Band and multi-angular

b) Computing parameters using time-series regression is not possible due to low revisit interval of Sentinel and time mismatch of swath overlap of SMAP and Sentinel

c) The Active-Passive Algorithm is modified to accommodate the snapshot and work in the emissivity space, as shown below.

Radiometer Brightness Temperature

Surface Temperature SAR co-pol backscatter SAR x-pol backscatterand Algorithm parameters

SMAP (L-Band) Sentinel 1A/1B (C-Band)

SMAP TB Gridded at 9 km

Sentinel co-pol and x-pol observations

Disaggregated TB at 3 km Retrieved Soil Moisture from Disaggregated TB at 3 km

Data Flow: Baseline L2_SM_SP Algorithm

Note: It is a moving window 33 km domain is used for disaggregation to conform with the L2_SM_P_E.

SMAP (L-Band) Sentinel 1A/1B (C-Band)

Sentinel co-pol and x-pol observations

Disaggregated Soil Moisture at 3 km

Data Flow: Option-1 L2_SM_SP Algorithm

SMAP Soil Moisture Gridded at 9 km

Note: It is a moving window 33 km domain is used for disaggregation to conform with the L2_SM_P_E.

With the present data stream of Sentinel 1A and 1B, it is expected to get a global coverage in every 12 days.

Twelve Days Coverage of SMAP-Sentinel high resolution soil moisture data from 1st May, 2017 to 12th May, 2017

SMAP-Sentinel-1 AP Soil Moisture Results

The above image shows that SMAP-Sentinel does capture finer details and the overall pattern is similar to what observed by SMAP AP retrievals

3 [km] SMAP Radiometer + Sentinel Radar

May 17th, 2015 over Southern Canada in Manitoba

9 [km] Gridded SMAP Radiometer-based Soil Moisture

SMAP Active-Passive Soil Moisture Product at 3 km

Data Driven Beta Retrievals

-- Retrieved Beta from the Radiometer and Radar Data

-- Brightness Temperature of Radiometer (K)-- Surface Temperature (K)-- Vegetation Opacity parameter-- Albedo-- SAR co-pol data-- SAR x-pol data-- Parameter derived from SAR co-pol and x-pol data

The physically-based retrieval procedure of β accounts for the effects of vegetation/roughness on emission as well as on backscatter.

This approach does not require time series.

8T. Jagdhuber1, M. Baur2, N.N. Das3, D. Entekhabi4, M. Link1,5, 2016, Physically-based Retrieval of Active-Passive Covariation Parameter β for the SMAP Mission. To be submitted to TGARS.

Beta Retrievals from V and vv combination, averaged over 84 days

Beta derived from Time seriesFrom V and vv combination

Beta Retrieval Evaluate against the 84 days of SMAP Active and Passive Data

[-]

New Beta Retrievals

SMAP-Sentinel BETA Evolution over Global Domain

[-/-]

[-/-]

Mean

Coefficient of Variation (CV) in

High CV indicatesSeasonality in Beta

Beta goes to zero with increasing density of vegetation

Grassland

Dependence of Beta on Incidence Angle of Sentinel Data

Cropland

Shrubland Savanna

The mean Beta values show clear dependence on Sentinel data incident angle.

Evaluation: Comparison with Airborne Data

Airborne L-band SMAPEx during 2015 in the Southeastern Australia

Urban area

Urban area

Urban area

Waterbody

Urban area

Waterbody

The SMAPEx Domain

SMAPEx Domain 2015, TBv, 05-05-2015

1 km, EASE GRID[K]

Expected error in the SMAP TBv is ~3 to 4 [K] due to incidence angle correction

The Airborne L-band radiometer shows minimal impact due to manmade structures

Sentinel vh

Sentinel vv

05-05-2017

Small Ponds and Manmade Structures

Urban Areas

Manmade Structures Urban Areas

Urban Areas

Significant Impact of urban areas and water bodies are found in the high-resolution Sentinel (vv and vh) observations

1 km, EASE GRID

[-] [-]with Median Filter of [3X3]

Approach to Mitigate Impact of Manmade Structures and Water Bodies (05-05-

2015)

Sentinel vv Sentinel vv

[-] [-]

Sentinel vh Sentinel vh

1 km, EASE GRID

1 km, EASE GRID

1 km, EASE GRID

1 km, EASE GRID

Examples of Median Filtering (05-05-2015)

Mitigation of Outliers in the Sentinel Observations

Limited Mitigation of Outliers in the Sentinel Observations

Before Filtering After Filtering

SMAPEx TBv Obs at 3 kmSMAP-Sentinel AP and L2_SM_P_E (05-05-2015)

SMAP_Sentinel TBv at 3 km

[K]

L2_SM_P_E Gridded at 9 km

Minimum Performance

Average VWC in the SMAPEx Domain is ~1 kg/m2

Summary of Validation Statistics of SMAP_Sentinel L2_SM_SP vs SMAPEx

Date: 05-05-2015

L2_SM_SP vsSMAPEx (slope)

L2_SM_SP vsSMAPEx

(R)

L2_SM_SP vsMin-Perf(slope)

L2_SM_SP vsMin-Perf

(R)

Total at 3 km 0.46 0.48 0.12 0.36Total at 9 km 0.42 0.62 0.15 0.46

Date: 09-13-2015

L2_SM_SP vsSMAPEx (slope)

L2_SM_SP vsSMAPEx

(R)

L2_SM_SP vsMin-Perf(slope)

L2_SM_SP vsMin-Perf

(R)

Total at 3 km 0.48 0.55 0.22 0.45Total 9 km 0.60 0.69 0.37 0.58

SMAP_Sentinel Product Comparison with Core Validation Sites

Minimum 3 number of in situ stations required to be a Core Validation Site at 3 km

BL: Baseline Opt-1: Option 1MP_BL: TB without DisaggregationMP_Op: SM without Disaggregation

Core Site: TxSONDate: 2016-10-25

Black: Use recommended [Retrieval Quality Flag bit(0)=0]Gray: Retrieval attempted and succeeded but use not recommended [bit(0)=1, bit(1)=0, bit(2)=0]Green: Retrieval attempted but failed [bit(0)=1, bit(1)=0, bit(2)=1]Cyan: Retrieval not attempted [bit(0)=1, bit(1)=1]

Climate class: Temperate (Cfa)Landcover: Grasslands

Soil texture:S-%: 41C-%: 27BD: 1.48

TxSON (Core Pixel)

Not for public release or redistribution. This document has been reviewed and determined not to contain export controlled technical data.

Alg ubRMSE Bias RMSE R

BLOpt-1MP_BLMP_Op

0.0290.0320.0380.039

-0.028-0.016-0.015-0.028

0.0410.0350.0400.049

0.9210.9240.9650.966

Core Site: ValenciaDate: 2016-03-23

Black: Use recommended [Retrieval Quality Flag bit(0)=0]Gray: Retrieval attempted and succeeded but use not recommended [bit(0)=1, bit(1)=0, bit(2)=0]Green: Retrieval attempted but failed [bit(0)=1, bit(1)=0, bit(2)=1]Cyan: Retrieval not attempted [bit(0)=1, bit(1)=1]

Climate class: Arid (BSk)Landcover: Croplands

Soil texture:S-%: 19C-%: 49BD: 1.40

Valencia (Core Pixel)

Not for public release or redistribution. This document has been reviewed and determined not to contain export controlled technical data.

Alg ubRMSE Bias RMSE R

BLOpt-1MP_BLMP_Op

0.0340.0330.0330.032

0.013-0.001-0.014-0.003

0.0370.0330.0360.032

0.5160.5310.4250.514

Core Site: Yanco

Date: 2016-03-12

Black: Use recommended [Retrieval Quality Flag bit(0)=0]Gray: Retrieval attempted and succeeded but use not recommended [bit(0)=1, bit(1)=0, bit(2)=0]Green: Retrieval attempted but failed [bit(0)=1, bit(1)=0, bit(2)=1]Cyan: Retrieval not attempted [bit(0)=1, bit(1)=1]

Climate class: Arid (BSk)Landcover: Grasslands

Soil texture:S-%: 46C-%: 31BD: 1.44

Yanco (Core Pixel)

Not for public release or redistribution. This document has been reviewed and determined not to contain export controlled technical data.

Alg ubRMSE Bias RMSE R

BLOpt-1MP_BLMP_Op

0.0660.0590.0560.056

0.0590.0600.0390.030

0.0880.0840.0660.061

0.9180.9290.9290.929

Conclusions

• Comparisons with available airborne field experiment (SMAPEx) shows that L2_SM_SP does positively use Sentinel-1 information to provide high-resolution brightness temperature.

• Minimum Performance (in TB and soil moisture) confirm conclusions about impact of Sentinel information on soil moisture retrievals.

• Core Site comparisons at 3 km and 9 km are severely limited in number of sites and temporal samples at each site. They nonetheless show that the L2_SM_SP performs to target accuracy of the original L1 requirement.

• More spatial resolution (with respect to L2/3_SM_P_E) comes in a trade-off with accuracy. Utility is dependent on the application needs.

• SMAP-Sentinel Active-Passive Product (L2_SM_SP) is ready for Beta Release in couple of months.

Thank you

Acknowledgements: SMAP project, JPL Science Data System, and all the SMAPCal/Val partners.