Retreating Glaciers of the Himalayas: A Case Study of Gangotri Glacier Using 1990-2009 Satellite Images

Figure 6. 90-m resolution digital elevation model (DEM) acquired by the Space Shuttle
Endeavour during the Space Radar Topographic Mission (SRTM) in 2000.

3. Methodology
Before Landsat TM images can be digitally processed, they need to be calibrated using the
following equations to convert digital numbers (DN) into radiance and reflectance. These
conversions ensure that images acquired on different dates can be compared with one another
more accurately.
(L max,- L min) +min
L, = Qcal + L min 2
Qcal max
(=r * L *d2)
p cos 0B
ESUN
L = spectral radiance at sensor's aperture in W/(m2* sr*pm);
Qcai = quantized calibrated pixel value in DNs;
Qcalmax= maximum quantized calibrated pixel value (DN = 255) corresponding to
Lmax ;
Lmaxx = spectral radiance that is scaled to Qcalmax in W/(m2*sr*pm);
Lminx = spectral radiance that is scaled to Qcalmin in W/(m2*sr*pm);
6 of 11

Ding, Jennifer & Dong, Pinliang. Retreating Glaciers of the Himalayas: A Case Study of Gangotri Glacier Using 1990-2009 Satellite Images. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc84326/. Accessed April 20, 2014.