Processing steps for Sentinel-1 GRD product

[ABraun]

@akenney

What do you mean about classifying just a single image? If images aren’t comparable to other images unless you calibrate them, then what information would a classification be based on if you only have a single uncalibrated image? Do you mean classifying different parts of the same image relative to each other?

yes, for example classifying water bodies in the image.

@akenney

The documentation for the GRD product says the data has been “projected to ground range using the Earth ellipsoid model WGS84. The ellipsoid projection of the GRD products is corrected using the terrain height specified in the product general annotation.” What is the difference between this and the Range Doppler Terrain Correction / projecting into a coordinate reference system, which you mentioned as having not yet been done?

GRD products have square pixels and are more or less geometrically correct regarding their geolocation. However, this only works for flat areas. If you have topography in your image, the incidence angle of the imaging system causes geometric distortions. These can be corrected with a digital elevation model. Some more notes on this: The reason of range doppler terrain correction?

@akenney

f spatial resolution is important in my particular use case, does that mean I should use SLC rather than GRD, should not perform multi-looking but should probably do some type of speckle filtering? (I haven’t looked into the different types, but my understanding is that some are better than others at preserving fine-grained detail.)

If you need the image in its original form, SLC offers you the most options, yes. GRD products are ready to use but they were already processed in a way which could have diminished the information you need. But SLC data do not necessarily contain more details.

[quote=“akenney, post:3, topic:16957”]For context, what I’m trying to do is agricultural crop cycle monitoring, of areas that are on the order of a few thousand square meters.
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I personally would stick to the GRD products then. They are fine regarding their spatial resolution (10x10 m) and you can quickly generate timer-series of data by calibrating the products to Sigma0. The temporal aspect should give you more information than the pure pixel resolution.