After the geometric correction, i am obtaining negative values in remote sensing reflectance (Rrs). Can someone explain the reason for it? Is there any scientific significance for negative values in Rrs?
Hi Srinivas,
Which atmospheric model have you used ? for which images ?
If you have a very low radiance value (i.e. pixels in shade), then the atmospheric model you use could not be able to model the reflectance accurately and you can get some negative reflectance values. It just means for those pixels, the results are unreliable and therefore should be excluded.
I got the same problem with SPOT4 images, negatives values in few pixels in Red band and very high values (saturated pixels) in NIR band, we have excluded the negative values , see fig.8 in my paper:
Hi Srinivas,
I confirm what Nadia said: negative reflectances are meaningless. There are a couple of things you need to check: (1) were the data properly calibrated? (2) how did you apply an "atmospheric correction"?
If you'd like to elicit more responses from the community, you should provide more details about which data you are analyzing, where you got those from, how you processed them, which assumptions you made, which ancillary data you used, etc.
Good luck in your investigation. Michel.
Thank you Michel and Nadia,
The data i am using is HICO ( Hyperspectral Imager for Coastal ocean) and the atmospheric correction used is Tafkaa_6S(mentioned in the HICO sensor website).. The HICO data is processed using an online tool present in the sensor website.
Srinivas, you just check with elevation parameter in the atmospheric correction model. Try by the average height of the features in the whole image.
Yes, when we speak about water body, it gives low reluctance across visible spectrum of EMR, Those target provided less reflectance contains negative values or if there is error in detectors array like striping error provided negative values of reflectance.
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