Methods

The geographical extent of this study spanned the Chiang Mai province in Northern Thailand.

To study the practice of slash-and-burn agriculture in Northern Thailand in comparison to changes in vegetation cover and greenness, infrared bands from ETM+ images must be examined to create a Normalized Difference Vegetation Index.  Because slash-and-burn involves fires, We downloaded "MODIS/Terra Thermal Anomalies/Fire 8-Day L3 Global 1km SIN Grid V005" from NASA's Reverb | Echo website to visually diagnose the extent of fires in two different time periods, year 2001 and 2006, and note any significant changes.

In terms of spread, we must first understand the topography of the region.  Because fire spreads uphill, hilly and mountainous regions will facilitate a spread in extent of an existing fire.  To document this, ETM+ data was downloaded from the University of Maryland's Global Land Cover Facility site on Thursday, Nov. 10, 2011.  Our data was processed through the ENVI software to generate NDVI data and create a grayscale model of elevation for a 3-dimensional model.  We then compared two different projections from April 9, 2001 and February 18, 2006, and any difference (increase or decrease) was noted.

Ancillary data included images of the study area taken from Google Earth and FIRMS Firefly.  Google Earth was used as a tool to locate, examine and support our analysis of the study area.  The FIRMS Firefly engine was used as an additional tool to verify and/or dispel MODIS data.


SPECIFIC STEPS FOR ANALYSIS:

Downloading ETM+ data of the study area:

1. Visit the Global Land Cover Facility website from the University of Maryland to access and download map files.
2. On the right column labeled "Download Data", click the link "ESDI".
3. Click the picture labeled “Map Search” to search via a world map.
4. On the left column, choose desired dataset (ie. ETM+, ALI).
5. Search by place by choosing "Place" above the map.
6. In the "Place" search bar, type in place name (ie. "Chiang Mai, Thailand").  Choose "Preview & Download" to choose one from a series of images of that region.

Downloading MODIS data of the study area:

1. Access NASA’s Reverb | Echo website.
2. Under “Spatial Search”, zoom into interested study area (in this case, Northern Thailand); click and drag to set a bounding rectangle.
3. Under “Search Terms”, type “MODIS Fire” to get results that are related to fire and burned area.
4. Under “Temporal Search”, choose the start and end dates of data parcels for the time period of interest. For instance, input 2001-04-01 00:00:00 to 2001-04-30 11:59:59 for data in April 2001. Repeat for other months/years of interest for comparison.
5. Under “Step 2: Select Datasets”, choose the dataset of interest. In this study, “MODIS/Terra+Aqua Burned Area Monthly L3 Global 500m SIN Grid V005” was chosen to analyze all burned areas per month.
6. “Search for Granules” and accept REVERB’s pop-up notification. 
7. Use the "View spatial extent" button of each granule and the map to see its geographical extent.  If you know the spatial extent of your study area, look for files whose third portion of their name match the tile indices of your study area.  For instance, Northern Thailand is in the 27th column and the 7th row, denoted as "h27v27".  For a map of all tiles in the MODIS Sinusoidal Projection, visit this site: http://remotesensing.unh.edu/modis/modis.shtml.  For more information on the nomenclature of each MODIS data file, consult the MCD45 Burned Area User Manual version 2.0.
8. Click the "Add to cart" button for files to be downloaded.  Click "View Items in Cart" when finished.
9. To download the data files, select all and choose "Download selected" in "Text File".
10. Open the Text File and copy-and-paste the URLs beginning with "ftp://" in your browser's URL bar, and hit Enter to save them to your disk.

Opening and analyzing MODIS .hdf files downloaded from "Reverb | Echo" in ENVI:

1. Go to the Power Bar, and choose "File" > "Open External File" > "Generic Formats" > "HDF".
2. Open the .hdf file of interest.  Load "Burned Area" to analyze which areas experienced fire and when.  Load in Grayscale from the "Available Bands List".
3. Go to the toolbar of the display containing the image of "Burned Area" and choose "Enhance" > "[Image] Linear 0-255" to improve the visibility of burned areas.
4. Right click on the image and choose "Cursor Location/Value...".
5. The value following "Data:" is the approximate Julian date of burning.  The legend (as seen in page 6 of the MCD45 Burned Area User Manual version 2.0) is as follows :
• 0 = unburned
• 1-366 = approximate Julian date of burning
• 900 = snow or high aerosol
• 9998 = water bodies (internal)
• 9999 = water bodies (seas and oceans)
• 10000 = not enough data to perform inversion throughout the period
• Julian dating is used by scientific and astronomy communities to denote a date in the calendar year.  For instance, a Julian date of 45 denotes the 45th day of the year, or February 14.  See this website for a useful converter: http://aa.usno.navy.mil/data/docs/JulianDate.php.
• In the MODIS file name, date is denoted as "AYYYYJJJ", where "YYYY" is year and "JJJ" is Julian date.
6. Hover cursor over the image to find areas that are unburned or burned and when the fire occurred.
7. Match with a spectral image of the study area to assist in finding agricultural areas, or vegetation indices (ie. NDVI) to discover changes in vegetation cover possibly due to fires, or an elevation model to analyze vulnerability of spread (fires spread uphill).