Geoscience Reference
In-Depth Information
(DN) values in
HYP
. h e radiance is the power density scattered from the
earth in a particular direction and has the units of watts per square meter
per steradian (Wm
-2
sr
-1
) (Richards 2013). h e EO-1 User Guide (v. 2.3)
provides the necessary information on these conversions in its
Frequently
Asked Questions
(FAQ) section (Beck 2003). According to this document,
the radiance
HYPR
for the visible and near-infrared (VNIR) bands (bands 1
to 70) is calculated by dividing the digital number in
HYP
by 40. h e radiance
for the shortwave infrared (SWIR) bands (bands 71 to 242) is calculated by
dividing
HYP
by 80.
HYPR(:,:,1:70) = HYP(:,:,1:70)/40;
HYPR(:,:,71:242) = HYP(:,:,71:242)/80;
For quantitative analyses, the radiance values
HYPR
need to be corrected for
atmospheric and topographic ef ects. h is correction, which yields earth
surface rel ectance values (in percentages), is beyond the scope of the topic.
h e EO-1 User Guide (v. 2.3) again explains several methods to convert
radiance to rel ectance values (Beck 2003). A simple way to convert radiance
to rel ectance for relatively clear Hyperion images is given in
https://eo1.usgs.gov/faq/question?id=21
We will instead process the Hyperion image to create a georeferenced RGB
composite of bands 29, 23 and 16, to be used in i eldwork. h e header
i le
O1H1690582013197110KF.HDR
contains (among other things) the
wavelengths corresponding to the 242 spectral bands. We can read the
wavelengths from the i le using
textscan
:
fid = fopen('EO1H1690582013197110KF.hdr');
C = textscan(fid,'%f %f %f %f %f %f %f %f',...
'Delimiter',',','Headerlines',257,'CollectOutput',1)
fclose(fid);
h is script opens the header i le for read only access using
fopen
and dei nes
the i le identii er
fid
, which is then used to read the text from the i le with
textscan
, and to write it into the array
C
. h e character string
%f %f %f %f
%f %f %f %f
dei nes the conversion specii ers enclosed in single quotation
marks, where
%f
stands for the double-precision l oating-point 64-bit output
class. h e parameter
Headerlines
is set to 257, which means that the i rst 257
lines are ignored when reading the i le. If the parameter
CollectOutput
is 1
(true),
textscan
concatenates output cells of the same data type into a single
array. Function
fclose
closes the i le dei ned by the i le identii er
fid
. h e
array
C
is a cell array, which is a data type with indexed containers called
cells. We can easily obtain the wavelengths from
C
using
