Lab Instructions
Lab 7, due 5:30 am Oct 30, 2007
EES5053/ES4093: Remote Sensing, UTSA
Student Name: ___________________
Calculate Temperature from ETM+ Image
Purpose
In this lab, you will get a sense about IDL. You will use IDL to compute
the temperature of a Landsat image, and analyze the distribution of
temperature.
Part I: Concepts and short questions:
1. summarize the similarities and differences between real aperture radar and synthetic
aperture radar as detail as possible (not necessary just from the lecture notes)
2. explain the similarities and differences between reflectivity and radar backscatter
3. explain backscatter coefficient and parameters affecting it. You may refer to this
website for a better and detailed explanation:
http://earth.esa.int/applications/data_util/SARDOCS/spaceborne/Radar_Courses/Radar_C
ourse_III/parameters_affecting.htm.
4. give two active radar systems and explain them in detail (in terms of wavelengths or
frequencies, resolution, repeatability, launched time, application, etc.)
Part II:
1. Preparation:
(1). Copy the data directory Lab7 in the server
(\\129.115.25.240\XIE_misc\Fall2007-RS\ to c:\Fall2007-RS\YourName\
2. Introduction
As you learned, landsat ETM+ image has 9 bands, band 1-3 is visible
bands, 4-5 and 7 is near and short wave infrared band, band 8 is panchromatic
band, band 6 and band 9 is thermal band. Band 6 is low gain thermal band and
band 9 is high gain image. *.H2 is the header file of thermal bands. These two
thermal bands are what we need to derive the temperature of land surface. You
can check the difference of these two images by linking them or performing the
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statistics. The DN is actually different. You are required to compare the
difference of brightness/surface temperature in this lab. The image you will work
on is p027r040, acquired on March 21, 2003.
Open image LE7027040000308050.H2 in ENVI. Band 1 is the band 6 (low gain)
of the ETM+ image, and band 2 is band 9 (high gain) of the image. Display band
2 using gray scale.
3. Calculate the temperature using IDL
Equations (4) to (6) are used to covert the DN to Radiance, then Radiance to
brightness temperature, and finally compute the surface temperature from
brightness temperature. Detail information about the equations are included in
the article: LST.pdf (Weng et al. 2004) in your Lab 7 folder. If you are interested
in, you should read this paper in more detail and you should be able to do a class
project using this topic as well. In this code, we only use a single emissivity of
0.988. If you want to do a completed project, you should use the method from the
paper.
Click IDL, and go to File -> New -> Editor. Copy this code below to your IDL (similar
as figure 1) and saved as temper.pro, or directly open the temper.pro in your Lab7 folder
into IDL.
PRO temper
; calculate temperature of an Landsat image
envi_select, title='Choose multispectral image', fid=fid, dims=dims, pos=pos
if (fid EQ -1) THEN BEGIN
PRINT, 'cancelled'
RETURN
ENDIF
num_cols=dims[2]-dims[1]+1
num_rows=dims[4]-dims[3]+1
;num_bands=n_elements(pos)
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;num_pixels=num_cols*num_rows
image=envi_get_data(fid=fid, dims=dims, pos=pos[0]) ;pos[0] is the first band, pos[1]
the second band, ...
L=temporary(0.0370588*image+3.2)
;calculate radiance of high gain image
;L=temporary(0.066823*image)
;calculate radiance of low gain image
TB=temporary(1282.71/(alog((666.09/L)+1)))
;calculate brightness temperature
RT=temporary(TB/(1+(0.0007991666*TB)*alog(0.988)))
;supposing the same emissivity of 0.988
envi_enter_data, RT
END
Then compile it and run it. The Choose multispectral image window of ENVI
will appear. Click the Spectral Subset, you will see a window as below. Check the
6H (high gain image). Then the resulting temperature image of high gain will be
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appeared as Memory 1 in the Available Band List window of ENVI. You may
save this memory image as a real image. Open this image, the pixel values are
temperature and unit is in Kelvin.
In order to do the low gain image, what you need to do is to change this
L=temporary(0.0370588*image+3.2)
;calculate radiance of high gain image
;L=temporary(0.066823*image)
;calculate radiance of low gain image
To
; L=temporary(0.0370588*image+3.2)
;calculate radiance of high gain image
L=temporary(0.066823*image)
;calculate radiance of low gain image
Then select the 6L (low gain) image as input. The resulting temperature image will be
appeared as Memory 2 in the Available Band List window of ENVI.
Questions (1): Compare the DN difference of low gain (band 1) and high gain
(band2). (10 points).
Questions (2): Compare the Temperature difference of low gain and high gain.
(10 points).
Questions (3): Analyze the distribution and variability of the Temperature (high
gain) for the entire image area. To assistant your analysis, you may use the
multispectral (visible and near infrared) false color or true color image. You
should be able to download the image from TexasView website or directly click
http://data.crgsc.org/sensor/l7/p027/r040/y2003/d080/nlaps/. Download the .H1,
.I1, I2, I3, I4, I5, I7. You can then open the H1 in ENVI, which will open the Band
1,2,3,4,5,7 as one image file. A road center line vector file provided in the folder
can also help you to familiarize yourself the locations. (80 points).
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Use histogram, statistics, density slice, link with false color display of
different bands composition, and others to analyze the distribution and variability
of temperature for the entire area. For example, do you see any heat island in the
downtown San Antonio area in this time of year (March)?
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