Yu-Ting Yu
New Member
Posts:2  
| 28 Mar 2022 10:35 AM |
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Hi,
I was working with WorldView 3 SWIR data. For some reason, many areas of my SWIR data will be removed after I apply Radiometric Calibration in ENVI 5.6. When I say "remove", I mean the area have information in the original data and it became blank after calibration.
The product was obtained from L3Harris, originally from Maxer I think. The SWIR band was storage in 11-bit from 1 to 2047. Based on the metadata, the product type was "Basic 1B". The followings are the product description from the agency that we buy the product from.
Product Description: WorldView-3 SWIR Select Collection
License: Academic Internal Use
Product Type: 3.7m SWIR Band
Geometric Processing: Orthorectified (Level 3A)
Accuracy: 10 m CE90
Projection (coordinate system); Datum; Units: UTM; WGS84; Metric
Resampling Kernel: 2x2 Bilinear
What might be the reason for those data removal after Radiometric Calibration?
Although I have hear that QUAC can directly be implied on data without radiometric calibration, I don't want to deploy QUAC directly since the radiometric have some primary role for our research. In this case, is there any suggested way for doing radiometric calibration? such as settings or formula for band math?
Thanks!
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MariM
Veteran Member
Posts:2396 
| 30 Mar 2022 08:03 AM |
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It sounds like you do not have access to the original data (we do not provide data - only software) so it could be that there was pre-processing performed that has altered the data in such that the resulting calibration does not return values within the expected range. You would need access to the original data to really know if the calibration is performed properly..
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Yu-Ting Yu
New Member
Posts:2
| 30 Mar 2022 08:04 PM |
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Yes, the data that I was using was crop to fit the ROI by the provider. Do you mean the provider also change the way that the data was storaged?
If I will be able to work with raw data. Does ENVI 5.6 support Radiometric Calibration for WV03 SWIR data? or you'll suggest using the Band Math tool with formulas to make calibration?
For formulas, I mean:
DN to ToA radiance : L = GAIN * DN * (abscalfactor / effectivebandwidth) + offset
ToA radiance to ToA reflectance: R = (L * d_es^2 * pi) / (E_sun * cos(theta))
Thanks!
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MariM
Veteran Member
Posts:2396
| 31 Mar 2022 06:53 AM |
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Yes ENVI will calibrate data that have the appropriate information in the header file. This is why it is best to use the original data. Some of the data you were using was mosaicked data. Data should in general be calibrated prior to mosaicking unless the data were taken in succession at the same day/time. If you mosaic images from different dates/times before, then the metadata of only one of the images in the mosaic is used for all images, which may not be correct and can result in values falling near or below 0. If the values are zero or less, then they will be set to 'nodata' in the result.
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Yu-Ting Yu
New Member
Posts:2
| 05 Apr 2022 04:14 PM |
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Hi,
Turn out the product provider inform us that they actually made some mistake and the values in the data were truncated. The areas of 'nodata' were significantly reduced by using new data for Radiometric Calibration in ENVI 5.6. However, there are still some parts presented 'nodata' after radiometric calibration, mostly waterbody or mountain shadow. For those areas/pixels without any SWIR band data after radiometric calibration, will you suggest me to mask them when I apply QUAC for the next step?
Thank you.
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