| Bits & Bytes [message #57898] |
Tue, 08 January 2008 03:46 |
jujo
Messages: 8
Registered: May 2007
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Junior Member |
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Hello there...
I'm sorry if my question is too basic. I'm working with 8 bits Spot
Vegetation images. I have two bands:
1-NDVI data
2-Status Map (information about clouds, water, snow...)
I need to apply the status map on the NDVI data, because I need to
flag cloud and snow pixels.
Below I have some information about the status map.
From MSB to LSB
Bit NR 7 (MSB): radiometric quality for B0 coded as 0 if bad and 1 if
good
Bit NR 6: radiometric quality for B2 coded as 0 if bad and 1 if good
Bit NR 5: radiometric quality for B3 coded as 0 if bad and 1 if good
Bit NR 4: radiometric quality for MIR coded as 0 if bad and 1 if good
quality
Bit NR 7 - 4: coded as 0 for 'no data', missing lines, sea on VGT-S
products, adjacent blind or defective MIR detectors, interpolated
data, saturated data, negative data after atmospheric correction
Bit NR 3: land (code 1) or water (code 0), computed from the "Digital
Chart of the Worlds"
Bit NR 2: ice/snow (code 1) , code 0 if there is no ice/snow, computed
from thresholds from reflectances
Bit NR1: 0 0 1 1
Bit NR0: 0 1 0 1
(LSB): clear shadow uncertain cloud
My question is: how can I use the status map to flag cloud and snow
pixels? I'm reading them into ENVI, but I can't understand the byte
numbers.
Any comments very welcome.
Best!
Jurandir
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