Landsat 7 Gain Setting Strategy, as of September 2000

The currently implemented gain setting strategy for Landsat 7 consists
of a fixed categorization of the surface cover types of the earth and
gain setting rules that are surface cover and sun angle based. The gains
for bands 1-3 are currently always changed together as are the gains for
bands 5 and 7.

The earth surface categories are as follows:

> a\) Land (non-desert, non-ice)
>
> http://ltpwww.gsfc.nasa.gov/IAS/word_files/l7_global_land.doc (Word)
>
> http://ltpwww.gsfc.nasa.gov/IAS/pdfs/l7_global_land_doc.pdf (PDF)
>
> b\) Desert
>
> http://ltpwww.gsfc.nasa.gov/IAS/ascii/desert.lst (ASCII)
>
> c\) Ice/Snow
>
> http://ltpwww.gsfc.nasa.gov/IAS/ascii/arctic.lst (ASCII)
>
> (see Table 1 of the land database for Antarctica)
>
> d\) Water
>
> e\) Sea Ice
>
> (see Table 1 of the land database)

f)  Volcano/Night

> (see Table 6 of the land database)

Each Landsat-7 Path/Row of the Worldwide Reference System (WRS) is
categorized into one of these six types.

For each surface cover type the gain setting rules are different and are
listed below. The gains are calculated on a daily basis (prior to this
they were calculated on a monthly basis). The base value of the gains
are the default settings. These are found in
http://ltpwww.gsfc.nasa.gov/IAS/ascii/defgains.lst (ASCII)

Gain setting rules:

1)  Land (non-desert, non-ice; does include coral reefs):

2)  Bands 1-3 set to high gain

3)  Band 4 set to high gain except where sun elevation is greater than
    45°(then is set to low gain) --- to avoid dense vegetation
    (reflectance \> 0.66 ) saturation. (At this sun angle high gain in
    band 4 saturates at about a reflectance of 0.66, so switching to low
    gain keeps targets at this reflectance or below from saturating.)

4)  Bands 5-7 set to high gain

5)  Band 8 set to low gain

6)  Desert:

7)  Bands 1-3 set to high gain except where sun elevation is greater
    than 28° - to avoid bright desert target (reflectance \>0.65 in band
    3, \[\>0.66 in band 1 , \>0.71 in band 2\]) saturation

8)  Band 4 set to high gain except where sun elevation is greater than
    45°(then is set to low gain) --- to avoid bright desert (reflectance
    \> 0.66 ) saturation.

9)  Band 5,7 set to high gain except where sun elevation is greater than
    38° - to avoid bright desert target (reflectance \>0.70 in band 5,
    \[\>0.68 in band 7\]) saturation

10) Band 8 set to low gain

11) Ice/Snow and Sea Ice:

12) Bands 1-3 set to high gain except where sun elevation is greater
    than 19° - to avoid snow ice (reflectance \> 0.95 in band 3, \[
    \>0.94 in band 1, \>1.03 in band 2\]) saturation.

13) Band 4 set to high gain except where sun elevation is greater than
    31° - to avoid snow/ice (reflectance \>0.92) saturation.

14) Band 5, 7 set to high gain

15) Band 8 set to low gain

16) Night (nighttime imaging (sun elevation \<0) is only routinely
    performed for sites identified as "Volcano"):

17) Bands 1-4, set to high gain

18) Bands 5,7 set to low gain to reduce saturation of volcanic hot spots
    and fires

19) Band 8 set to low gain

The actual saturation reflectances corresponding to a given sun angle
are influenced by the Earth-Sun distance, which varies by ±1.5% over the
year producing a ±3% irradiance variation. The current implementation
does not incorporate this variability.

Band 8 is in low gain for all routine acquisitions as the noise level in
this band is such that high gain provides very little improvement in
performance. This implementation is currently under review and the band
8 gain settings may be altered in the future.

Maps applying to the first day of each month are found at:
(http://ltpwww.gsfc.nasa.gov/IAS/handbook/powerpoint/defgains_4.0.ppt)