Lab5# 2/12/2009, due 2/19/2009 before the class.
Remote Sensing in Hydrology, Spring 2009
Batch Processing MODIS Data and Snow Cover Change Analysis
Purpose:
This lab includes two parts. The first part tries to help you to know how to get MODSI snow cover data and analysis snow distribution and change. In the second part, you will learn how to batch process the MODIS data and combine daily Terra and Aqua data.
Part1:
Step 1: preparation
· Download two month MODIS/Terra 8-day snow cover products (MOD10A2) (November and December, 2008) from
https://wist.echo.nasa.gov/api//u218495/u218510/u218525/u219184/u219320/u219709/u219768#SCROLL, by checking MODIS/Terra in Cryosphere and clicking “MODIS/Terra Snow Cover 8-Day L3 Global 500m SIN Grid v005” in the “Choose Data Sets” window (see figure 1 below).
Figure 1
In the “Choose Search Area” part (see figure 2), checking “Type in Lat/Lon point”. We want to find some image in the northwest United State. The Lat/Lon point is 44.9250/ -125.5153. Then in the “Choose a Date/Time Range” part, entering 2008-11-01 as start date and 2008-12-31 as end date. Then start search and order the data.
Figure 2
There are many other ways to do so. For example, you can also search the data using spatial coordinate (Figure 3), by entering the upper left: 49°5′30″,-124°51′12″, and the lower right 40°1′30″, -91°0′17, then entering dates and searching and ordering data.
Figure 3
Once the searching is done, you will see a list of files available for you to choose. Click one of the metadata and make sure you understand what those file names mean.
Question1: what is the meaning of the file name and how many files you got for the two months?
You need to order the data and select the “ftp” as the option for data delivery. Once the data is ready for you to download, you will be noticed by email. Then you can download the data.
Step 2: Convert the data from .hdr format to .tif format.
· Open the data in ENVI.: File-----Open image files----*.hdf
· Right click the file of “Maximum Snow Extent”---- Add selected to memory
· Save Memory 1 to .tif ,Right click “Memory 1”-----Save Selected Files to Disk---choose the output path and output file name
· Define the file name as *.TIF
· Repeat and convert all the files.
Step3: Analyze snow cover change
The MODIS snow cover image is a coded raster. Those coded integer values include 0 (sensor data missing), 1 (no decision), 11 (darkness, terminator or polar), 25 (land-no snow detected), 37 (inland water), 39 (ocean), 50 (cloud), 100 (snow-covered lake ice), 200 (snow), 254 (saturated MODIS sensor detector), and 255 (fill – no data expected for pixel) (Riggs et al., 2006).
· Use ENVI or ArcGIS to conduct the basic statistic analysis, reporting your results in percentage of each type in each image. Table below is an example show the snow and cloud percentage for some 2006 images
File Name / Snow percentage(%) / Cloud percentage(%)MOD10A1.2006305 / 26.6 / 2.9
MOD10A1.2006313 / 23.4 / 10.6
MOD10A1.2006321 / 15.8 / 3.9
MOD10A1.2006329 / 36.7 / 14.3
MOD10A1.2006337 / 31.0 / 9.2
MOD10A1.2006345 / 34.3 / 2.9
MOD10A1.2006353 / 42.3 / 6.0
MOD10A1.2006361 / 83.8 / 5.6
· Use excel or other tool to make figures to illustrate the time series change of each type and do necessary analysis about the changes.
· Output the snow cover map in ArcGIS. And copy and paste some of them into your homework.
Part2:
Step 1: preparation
· Order and Download any one month (for example the November 2008) MODIS daily Terra and Aqua snow cover product version 5 (MODIS/Aqua Snow Cover Daily L3 Global 500m SIN Grid V004 and MODIS/Terra Snow Cover Daily L3 Global 500m SIN Grid V005 )
· At your local computer, create your own folder “C:/lab5”.
· In this folder, create a subfolder “MOD10A1” and save all the MODIS/Terra Snow Cover Daily L3 Global 500m SIN Grid V004 in it. And create a subfolder “MYD10A1” and save all the MODIS/Aqua Snow Cover Daily L3 Global 500m SIN Grid V005 in it.
(Note: the IDL code directly working on the version 5 (.hdf format), so you do not need to convert the .tif file as you did on the part 1)
· Then create an empty subfolder named as “TAC”
Step 2: Run the IDL code
Download the IDL code from \\129.115.25.240\XIE_misc\EES5093\Lab5 and copy it to your local Lab5 folder. This code is working to combine MODIS daily Terra and Aqua snow cover products and automatically create a new blended image with max snow and min cloud. This code includes three parts: (1) Transform original integers of MODIS to new codes, which including 6(snow), 5(ice), 4(water), 3(land), 2(cloud), 1(darkness, terminator or polar)，and 0(data missing). The bigger a code value is, the higher the priority class is. (2) Combined them using priority principle, which is the low-priority integer value is always replaced by a high-priority integer value. (3) Do statistics of the snow and cloud percentage of MOD10A1, MYD10A1 and Terra/Aqua Combined (TAC) snow cover maps.
· Open ENVI+IDL
· In the interface of IDL, choose “File—Open”. Compile the code.
· Run the code: “Run-Run TerraAquaCombined”. First choose all the MODIS Terra image then choose all the MODIS Aqua image. Only choose the ‘*.hdf’ files.
· Then exit.
Step3: Analyze the snow and cloud cover changes due to the combination
· In the folder “c:¥lab5¥TAC¥”, you can fine a .txt file named as “percentage.txt”. It includes the cloud (Pc) and snow (Ps) percentage of MOD10A1 and MYD10A1 and Terra/Aqua combined snow cover product.
· Plot them in figures and analyze the snow and cloud cover differences and changes of the three products. Use two figures to show the change of snow and cloud percentage respectively.
· Using the date on that Terra and Aqua combination makes the biggest cloud reduction as an example, output the snow cover maps of MOD10A1, MYD10A1 and TAC in that date and analyze the change spatially.
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