Lab exercise 3, due right before the class on Feb. 11, 2005
ES6973: Remote Sensing Image Processing and Analysis, UTSA
http://www.utsa.edu/eps/programs/EnvSci/HXie.htm

Student name: ______________

Download MODIS products and make comparison of ETM+ and MODIS temperatures

Purpose

            This lab is the second part of two labs about deriving temperature from  ETM+ image and comparing it with MODIS temperature. In this lab alone, you will learn how to download the Terra MODIS Temperature and Emmisivity product (MOD 11-Land Surface Temperature & Emissivity) of the same date as your ETM+ image. IDL code will be used to convert image to physical land surface temperature and emmisivity, and then the ETM+ temperature and MODIS temperature will be compared to see the difference. Once you finish this lab, you should be able to download any type of data from this EOS data gateway, and do some basic preprocessing using MRT and IDL/ENVI. Labs following this will help you further process your data and retrieve useful information from them.

Step 1. Preparation

          You will need to download the MODIS data from EOS data gateway at http://edcimswww.cr.usgs.gov/pub/imswelcome/. You can enter either as a guest or registered user. click MODIS/Terra under Land and MODIS/Terra Land Surface Temperature/Emissivity Daily L3 Global 1KM SIN GRID V004 as below.

Figure 1

        You have to define the approximately area you want and the date you want such as below

Figure 2

        Click Start Search, the system will search your order, and then list the resulting images you want such as below Figure 3: MOD11A1.A2002189.h09v05.004.2003243153318.hdf. MOD11A1 is the product name; A2002189 is the 189th day (July 8) of 2002; h09v05 is the MODIS tile number for the area (similar to the Path/Row of the Landsat Image); 004 is version 4. Figure 4 can help you to select which tile for your study area. Check the one you want, then click "Add selections to cart". It will bring the Figure 5 for you to choose the order option. Click "Choose Option", it will bring the Figure 6. Check the FtpPull and click OK. It will bring you Figure 7.

 Figure 3

Figure 4. MODIS tiles in Texas

Figure 5

Figure 6

Figure 7

Click the "Go to step 2: Order Form" of the Figure 7, you will be asked to fill the form of your information, then click "Submit Order Form", then your data will be ordered and an email notice will tell you that your order has been successfully submitted. A second email will notice you where to download the data once it is ready. Following the email instruction to download the data (two files) to your Data directory.

 Step 2. Use MRT tool to convert HDF to TIF

            MODIS Reproject Tool (MRT) can be opened through an icon called MODIS Tool in your desktop. Double click to launch it. You should be able to input the downloaded HDF file, then reproject it to UTM zone 13, 14, or 15 depending on your study area (see figure 8), and WGS 84 datum. the output cell size is 1000m. Save it as a GeoTIFF file to your MyWork directory. See an example in Figure 9, you only need to select 4 bands: LST-Day_1km, Emis_31, Emis_32, and Clear_day_cov, then click the Run to process. Figure 10 indicates the meaning of each name, and scale factor and offset for transferring the integer numbers to real physical numbers.

Figure 8, UTM zones of USA

Figure 9

Figure 10

Step 3. Stack the 4 MODIS images into one image using ENVI

        Load 4 MODIS images: LST-Day_1km, Emis_31, Emis_32, and Clear_day_cov into ENVI. Click File -> Save File As -> ENVI Standard, a new window is open. Click Import File to import 4 images in order (Figure 11), output to memory, click OK. Once finished, you will see a new file is listed in the Available Bands List window. the Band 1 is your LST, band2 is the Emis_31, band3 is the Emis_32, and band3 is the Clear_day_cov. You can open each of them to see the pixel values. These values will be transfer to physical values by using the above scale factor and offset. You can do this using Band Math, but in this lab, we will use the IDL code. when you see the code, you should know the parameters are from this Figure 10. Now I want to you to save the stacked file to a GeoTiff as you did in the Step 2 of Lab 2.

Figure 11

Step 4. Use IDL to convert the integer value to geophysical values

        As step 3 of Lab 2, you will copy the following code to IDL, compile, and run it. Make sure you change the names to match your defined input and output names and following the steps in step 3 of Lab2.

pro T2

Mte=READ_TIFF('C:\ES6973\MyWork\t-e.tif', CHANNELS=[0,1,2,3], geotiff=GTMODELTYPEGEOKEY)
        ;read the MODIS temperature and emmissivity file t-e.tif to Mte,
        ;and channel 0 is the LST, channel 1 is the Emis_31,
        ;Channel 2 is Emis_32, and Channel 3 is the Clear_day_Cov

Mt=temporary((Mte(0,*,*)*0.02))         ;convert integer numbers of MODIS LST to real physical values
Me=temporary(((Mte(1,*,*)+Mte(2,*,*))*0.002+0.98)/2.0)         ;final emissivity is the average emissivity
        ;of band31 and band32. convert integer number to physical number.
WRITE_TIFF,'mt.tif', Mt, geotiff=GTMODELTYPEGEOKEY, /FLOAT
WRITE_TIFF,'me.tif', Me, geotiff=GTMODELTYPEGEOKEY, /FLOAT

end

Step 5. Analyze and compare your results.

Open Mt.tif, Me.tif, and ETMt.tif in ENVI, make some analyses and comparison. report your major steps and results.