Geoscience Reference
In-Depth Information
wavelengths = C{1};
wavelengths = wavelengths';
wavelengths = wavelengths(isnan(wavelengths(:))==0);
We can now plot the radiance
HYPR
of the VNIR bands (blue) and SWIR
bands (in red) in a single plot.
plot(wavelengths(1:60),squeeze(HYPR(536,136,1:60)),'b',...
wavelengths(71:242),squeeze(HYPR(536,136,71:242)),'r')
According to v. 2.3 of the EO-1 User Guide (Beck 2003), Hyperion records
220 unique spectral channels collected from a complete spectrum covering
357 to 2,576 nm. h e L1R product has 242 bands but 198 bands are calibrated.
Because of an overlap between the VNIR and SWIR focal planes, there are
only 196 unique channels. Calibrated channels are 8-57 for the VNIR, and
77-224 for the SWIR. h e bands that are not calibrated are set to zero in
those channels.
In order to create an RGB composite of bands 29, 23 and 16, we can extract
the bands from the radiance values data
HYPR
by typing
HYP1 = HYPR(:,:,29);
HYP2 = HYPR(:,:,23);
HYP3 = HYPR(:,:,16);
To display the data with
imshow
we need convert the signed integer 16-bit
(
int16
) data to unsigned integer 8-bit data (
uint8
). For this purpose, we i rst
obtain an overview of the range of the data using a histogram plot with 100
classes.
subplot(1,3,1), histogram(double(HYP1(:)),100), title('Band 29')
subplot(1,3,2), histogram(double(HYP2(:)),100), title('Band 23')
subplot(1,3,3), histogram(double(HYP3(:)),100), title('Band 16')
As we see, the radiance values of most pixels from the spectral bands 29, 23
and 16 lie between 0 and 200 Wm
-2
sr
-1
. Several functions are available for
converting the data from
int16
to
uint8
. h e function
im2uint8
rescales the
data to the range [0,255] and of sets it if necessary. h e function
uint8
simply
rounds all values in the range [0,255] to the nearest integer; all values less
than 0 are set to 0 and all values greater than 255 are set to 255. h e function
mat2gray(A,[AMIN AMAX])
converts an arbitrary array
A
to an intensity image
I
containing values in the range 0 (black) to 1.0 (full intensity or white),
where
[AMIN AMAX]
can be used to limit the range of the original data, which
is scaled to the range [0,1]. Since most of our radiance values are within the
range [0,255], we use
uint8
to convert our data to the
uint8
data type without
losing much information.
