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I am a beginner in GEE. I am trying to create a model for SEBAL in GEE. I am stuck in a problem with LAI using SAVI. There is a problem with laio :(intermediate value).subtract is not a function

*function addLAI(image) {
    var laio = ee.Number(0.69.subtract(image.select('SAVI'))).log();
    var lai1 = laio.divide(0.59);
    var lai2 = lai2.divide(0.91).rename('LAI');
    return image.addBands(lai2)
}

What is the problem ?

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1 Answer 1

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Usually, the error messages "... is not a function" are caused by the use of a method that does not exist for a particular type of ee.Object or when the type of certain object is not clear for GEE and thus, needs a casting. In this case, the number needed a casting as ee.Number(0.69); however, since you want to generate an image with the subtraction of 0.69 and the SAVI value, you should instead use ee.Image.constant. Additionally, when defining lai2 you were calling a lai2 object that had not been defined; therefore, I assumed it should be lai1 instead of lai2. Here is the code that should perform the desired calculation.

function addLAI(image) {
    var laio = ee.Image.constant(0.69).subtract(image.select('SAVI')).log();
    var lai1 = laio.divide(0.59);
    var lai2 = lai1.divide(0.91).rename('LAI');
    return image.addBands(lai2);
};
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  • Thanks for your response, sir. I used your code, however, the result of LAI is homogeneous( my study area is UAE). Is it ok? Jul 26, 2022 at 4:38
  • The result should not be homogeneous, unless there is no spatial variation of SAVI. I recommend first checking if SAVI is spatially homogeneous, and start debugging the script from there. Jul 26, 2022 at 15:03

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