Different BT value at same pin and same incidence angle?


#1

Hello everyone,

I`m trying to obtain the BT_H and BT_V of the selected pin from SCLF1C or BWLF1C .

1.When I browsed the SM_REPR_MIR_SCLF1C_20120402T221253_20120402T230613_620_001_1.DBL with SNAP, the Pixel Info window displayed the BT_X,BT_Y,BT_H and BT_V at the incidence angle 42.49924 deg. Can you tell me how to calculate the value?


2.Then I browsed the SM_REPR_MIR_BWLF1C_20120402T221253_20120402T230613_620_001_1.DBL, the Pixel Info window displayed the BT_X,BT_Y of the same pin at the same incidence angle 42.5. But the value is different from above. I fell a little confused. Moreover, if i want to calculate BT_H and BT_V ,i need the Faraday Rotation Angle and Geometric Rotation Angle,right? And how to get it from BWLF1C?

Can you help me?

Thanks


#2

BT_X: data is from dataset “BT_Value_Real” filtered by (i.e. using only pixels acquired at) XX antenna polarisation
BT_Y: data is from dataset BT_Value_Real" filtered by YY antenna polarisation
BT_H and BT_V are BT measurements at ground polarisations HH resp. VV. These and their errors at ground are calculated according to Camps et al. (2005, Eqs. 13, 14; IEEE Geoscience and Remote Sensing Letters, 1545) where the rotation of the electric fields incident in the antenna plane is given by the difference of the Faraday and geometric rotations.

The BT data in the browse products is interpolated at an incidence angle of 42.5º from the MIRAS data in the ESA ground-segment processor, the data in the science product is not interpolated; all incidence angles are present. For display, the SMOS-Box interpolates the BT values on-the-fly to the 42.5 deg incidence angle, using only values with incidence angles between 37.5 and 52.5 degrees and the appropriate polarisation. So there might be small differences in the BT data between the science and the browse data display.
The browse products do not contain rotation angle data, you can not derive V and H polarisation from these products. Please also check the ESA documentation: https://earth.esa.int/documents/10174/1854583/SMOS_L1_Aux_Data_Product_Specification


#3

Dear marpet, thank you very much for your help:+1: