Empty output after running SARSim-Terrain-Correction

s1tbx
#1

Hi,

I’m trying to apply Terrain-Flattening and Terrain Correction to S1 GRD scenes using SNAP 7. Out of 10 scenes, 1 scene had empty output.

Full workflow:

Apply orbit file ==> Remote GRD Border Noise ==> Thermal Noise Removal ==> Calibration ==> Terrain-Flattening ==> SAR-Simulation ==> Cross-Correlation ==> SARSim-Terrain-Correction

Scenes with non-empty output:
S1A_IW_GRDH_1SDV_20190801T101449_20190801T101514_028374_0334DB_6CA1
S1A_IW_GRDH_1SDV_20190109T101238_20190109T101303_025399_02D02F_0606
S1A_IW_GRDH_1SDV_20190108T232857_20190108T232925_025392_02CFEE_A3B2
S1A_IW_GRDH_1SDV_20190106T112258_20190106T112323_025356_02CE8D_E219
S1A_IW_GRDH_1SDV_20190102T111147_20190102T111212_025298_02CC74_3132
S1A_IW_GRDH_1SDV_20190102T111212_20190102T111237_025298_02CC74_7A7A
S1A_IW_GRDH_1SDV_20190112T113154_20190112T113219_025444_02D1AB_7209
S1A_IW_GRDH_1SDV_20190108T120440_20190108T120505_025386_02CFA8_7CC1
S1A_IW_GRDH_1SDV_20190109T001121_20190109T001146_025393_02CFF3_4F22

Scene with empty output:
S1A_IW_GRDH_1SDV_20190123T095735_20190123T095756_025603_02D789_29D7

Does anyone know what causes this behaviour?

Regards,
Shobhit

#2

empty output means that the terrain effects simulated by SNAP could not be correlated with the terrain patterns in the image. Sometimes increasing the number of correlation points already solves the problem.

#3

I really appreciate your quick reply!

FYI, current parameters for cross correlation step.

      <numGCPtoGenerate>200</numGCPtoGenerate>
      <coarseRegistrationWindowWidth>128</coarseRegistrationWindowWidth>
      <coarseRegistrationWindowHeight>128</coarseRegistrationWindowHeight>
      <rowInterpFactor>2</rowInterpFactor>
      <columnInterpFactor>2</columnInterpFactor>
      <maxIteration>10</maxIteration>
      <gcpTolerance>0.5</gcpTolerance>
      <applyFineRegistration>true</applyFineRegistration>
      <inSAROptimized>true</inSAROptimized>
      <fineRegistrationWindowWidth>32</fineRegistrationWindowWidth>
      <fineRegistrationWindowHeight>32</fineRegistrationWindowHeight>
      <fineRegistrationWindowAccAzimuth>16</fineRegistrationWindowAccAzimuth>
      <fineRegistrationWindowAccRange>16</fineRegistrationWindowAccRange>
      <fineRegistrationOversampling>16</fineRegistrationOversampling>
      <coherenceWindowSize>3</coherenceWindowSize>
      <coherenceThreshold>0.6</coherenceThreshold>
      <useSlidingWindow>false</useSlidingWindow>
      <computeOffset>false</computeOffset>
      <onlyGCPsOnLand>false</onlyGCPsOnLand>

As per your suggestion, I’ll try increasing the numGCPtoGenerate value and share my results here.
Thanks again!