Lab exercise 4

This lab is to do an ETM+ radiometric correction, and transfer to reflectivity. the ETM+ reflectivity will then be compared with the MODIS reflectivity product.

We will use the Dark Subtraction to do a relative radiometric correction, but you are encouraging to explore the FLASSH and Empirical Line methods for an absolute radiometric correction if you will have enough time or you can do this in your term project. This lab also supposes your area is flat, however, if you would like, you can use a DEM to do a topographic correction, again, if you have time or you may do so in your term project. I would be happy to help you out in any way.

You will need to create a directory Lab4 under c:/UserData_ENVI. Please make copies for the images used or results you got in Lab 2 and Lab3, then delete them to free some space. You will need to create Data and MyWork subdirectories under Lab4. So You will need to download the needed data to Data, and your work to MyWork.

You will need to download the 6 reflectivity bands of a ETM+ image from the TexasView website at http://www.texasview.org/. This ETM+ image should be the same image as you used for Lab 2 in which you used its thermal band. Following the same step as you did in Lab 2 to download the files of *.H1, *.I1, *.I2, *.I3, *.I4, *.I5, and *.I7, which are band 1, 2, 3, 4, 5, and 7, respectively. Following the same steps in Lab 3 to download the MODIS/TERRA SURFACE REFLECTANCE DAILY L2G GLOBAL 500M SIN GRID V004. This is the MODIS reflectivity product (MOD09A1): daily and 500 m resolution. Then you use MRT and ENVI to reproject and stack them as you did in Lab3.

M1	T3	620-670
M2	T4	841-876
M3	T1	459-479
M4	T2	545-565
M5		1230-1250
M6	T5	1628-1652
M7	T7	2105-2155

MODIS band1-7 and spectral ranges, with corresponding ETM+ bands in the middle column

T1	M3	450-520
T2	M4	520-610
T3	M1	630-690
T4	M2	780-900
T5	M6	1550-1750
T7	M7	2090-2350

ETM+ band1-7 and spectral ranges, with corresponding MODIS bands in the middle column

In your report, please do a short discussion about the spatial, spectral, temporal, and radiometric resolutions of these two types of reflectivity bands. Use ENVI statistical tool to find the range of DN, which indicates you the radiometric resolution (range of numbers)

Get the minimum DNs of each bands of your stacked ETM+ image by using a Mask to mask the unwanted outside area. Those minimum values will be used as inputs for the Dark Subtraction for radiometric correction (see figure below). then the resulting image will be saved as a geotiff file for the IDL to use.

Click IDL, and go to File -> New -> Editor, and copy the following IDL code to the space, and save the file as radmcor.pro to C:\User_Data_ENVI\Lab4\MyWork. Please put some times to the code and try to understand the code a little bit, so you can do minimum modifications for your future work if you want. and you need to find the dr and sun elevation input to the right place when you read through the code. After you finish run this program, you can open your reflectivity file in ENVI for comparison.

pro radmcor
        ;this program is for radiometric correction

ETM=READ_TIFF('C:\UserData_ENVI\Lab4\MyWork\ETMp27r40y01m7d21.tif', CHANNELS=[0,1,2,3,4,5],   geotiff=GTMODELTYPEGEOKEY)
              ;read the Dark Subtraction correction image, you can comment this line while using the following
             ;two lines to pick up your file
;file=dialog_pickfile()
;ETM=read_tiff(file, CHANNELS=[0,1,2,3,4,5], geotiff=GTMODELTYPEGEOKEY)

arrdim=size(ETM, /dimensions)    ;get the dimensions of the ETM
cols=arrdim[1]
rows=arrdim[2]
rad=fltarr(6,cols,rows)   ;define a new float array with the same dimensions as ETM and 6 bands
ref=fltarr(6,cols,rows)

       ;calculate radiance, unit is W m^-2 sr^-1 um^-1, for the parameters: scale and offset
       ;of each band, please refer to Lab 4 of ES5053
rad(0,*,*)=temporary(0.775686*ETM(0,*,*)-6.2)
rad(1,*,*)=temporary(0.795686*ETM(1,*,*)-6.39999)
rad(2,*,*)=temporary(0.619216*ETM(2,*,*)-5.0)
rad(3,*,*)=temporary(0.965490*ETM(3,*,*)-5.10001)
rad(4,*,*)=temporary(0.125725*ETM(4,*,*)-0.99999)
rad(5,*,*)=temporary(0.043726*ETM(5,*,*)-0.35)

       ;calculate reflectivity, for the parameters of each band, please refer to Lab 4 of ES5053
      ;if you want do topographic correction, you will use complex equations here, and I can help you
dr=      ;please find it from Table 11.4 at http://ltpwww.gsfc.nasa.gov/IAS/handbook/handbook_htmls/chapter11/chapter11.html
theta=!pi*(90.0-sun elevation)/180.0      ;please find the sun elevation angle from the image head file

ref(0,*,*)=temporary((!pi*rad(0,*,*))/(1969*cos(theta)*dr))
ref(1,*,*)=temporary((!pi*rad(1,*,*))/(1840*cos(theta)*dr))
ref(2,*,*)=temporary((!pi*rad(2,*,*))/(1551*cos(theta)*dr))
ref(3,*,*)=temporary((!pi*rad(3,*,*))/(1044*cos(theta)*dr))
ref(4,*,*)=temporary((!pi*rad(4,*,*))/(225.7*cos(theta)*dr))
ref(5,*,*)=temporary((!pi*rad(5,*,*))/(82.07*cos(theta)*dr))

WRITE_TIFF,'C:\UserData_ENVI\Lab4\MyWork\reflec.tif', ref, geotiff=GTMODELTYPEGEOKEY, /float
;write the reflectivity to an image called reflec.tif

end

Use histogram, statistics, and others to analyze the distribution and variability of reflectivity for the entire area. and make comparison with the MODIS reflectivity (you need to convert the MODIS DN or scaled integers to reflectivity by multiplying the scale factor of 0.0001. you can use band math or using the IDL code in Lab3. IDL code needs to be modified to satisfy for this calculation). You can also do region of interest, and you may interpret the 500 meter MODIS image to 30 meter for matching the ETM+ image.

First calculate the NDVI from both ETM+ and MODIS reflectivity (using the red band and the first near infrared bands: band3 and band4 for ETM+ and band1 and band2 for MODIS). then do the similar comparison as step 4.

Write a report about the study area, the data, the method used, and your analyzing results, including the discussion mentioned in step 1.