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Earth Engine provides access to Aster level 1 Precision Terrain Corrected Registered At-Sensor Radiance -product (Aster L1T). I would be interested to reach the surface reflectance values of the image collection, to be able to use them in NDVI time-series analyses. Are there any algorithms ready for the processing steps needed?

  • DN to at sensor radiance. (radiance = ((DN - 1) * Unit Conversion Coefficient)
  • At sebor radiance to top of the atmosphere reflectance. (Can one use Landsat equation? This would require earth-sun distance and irradiance information)
  • Atmospheric corrections to reach surface reflectance. (any ready equations for aster data?)

For the first step I tried code below, but it returns Null values


    var dataset = ee.ImageCollection('ASTER/AST_L1T_003')  
                      .filter(ee.Filter.date('2014-10-01', '2014-10-30'))  
                      .filterBounds(AOI)  
                      .filterMetadata('CLOUDCOVER', 'less_than', 20);  


    // red and NIR channel digital numbers to at sensor radiance
    var radianceValues = function(img) {  
        var gainRED = img.get('GAIN_COEFFICIENT_B02');  
        var gainNIR = img.get('GAIN_COEFFICIENT_B3N');  
        var rad_RED = (img.select('B02') - 1) * gainRED;  
        var rad_NIR = (img.select('B3N') - 1) * gainNIR;   
        return img.addBands(rad_RED, rad_NIR);  
    };  

    // add red and nir band with radiance values  
    var radianceBands = dataset.map(radianceValues); 


  • You normally correct to TOA radiance than at-sensor reflectance. Final atmospheric correction using a radiative transfer model (eg., LaSRC, atcor) then results in earth surface reflectance. – Jeffrey Evans May 13 at 20:25
  • I am looking for SR of ASTER image collections in GEE as well. Haven't found any workable solution yet. Could you please share your findings with me once you got the corrections implemented? That would be great. regards Stefan – Stefan Peters May 15 at 2:30

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