MODIS Rapid Response System - Frequently Asked Questions

Frequently Asked Questions

Can I use an image from your gallery for...?
What do the red boxes mean?
What do the different band combinations mean?
What do the orbit track maps show?
How can I tell when MODIS will capture an image of my area?
Why do the real-time images look different from the gallery images?
How do I make true-color MODIS images?
Can you provide the full data file for an image I like in your gallery?
Can you send me geometrically corrected images and fire detections for my area of interest each day?
Do you produce fire detections at night?
What is the Julian day?
Where do you get the data used to draw political boundaries and coastlines on your gallery images?
Where can I find the georeferencing information for your subset and gallery images?
How do I use your subset and gallery images in my GIS or Image Processing software package?
How do I use the "Search by a keyword:" feature in your gallery?
How can I tell what time a subset image was acquired?
How can I set up a direct broadcast system to receive data from the MODIS sensor?
How do I convert to NDVI values from the colors in your NDVI images?

If you have additional questions, contact the MODIS Rapid Response Outreach Coordinator.

Can I use an image from your gallery for...?

All the images that appear on our site are in the public domain and can be freely used and reproduced for any purpose. Please credit the MODIS Rapid Response Project appropriately: "Image courtesy of MODIS Rapid Response Project at NASA/GSFC". For more information on use and credit, contact the MODIS Rapid Response Outreach Coordinator .

What do the red boxes mean?

The red boxes indicate the location of a thermal anomaly that was detected by MODIS using data from the middle infrared and thermal infrared bands. In most cases, this thermal anomaly is a fire, but sometimes it is a volcanic eruption, or even the flare from a gas well. We have no way of knowing which it is based on the MODIS data alone. In areas of known volcanic activity, we can verify an eruption using published reports of volcanic activity worldwide. The red outlines don't represent the actual size of the fire. They indicate the perimeter of 1km-resolution pixels containing the thermal anomaly detected by MODIS.

At right, thermal anomalies detected on the Kamchatka Peninsula, Russia. At top right is the heat signature from the Sheveluch Volcano; the remainder are fires.

Sheveluch Volcano and other thermal anomalies

What do the different band combinations mean?

A digital color image displayed on a monitor is composed of three different color channels: red, green, and blue. Satellite images are made by combining the reflected light detected by the sensor at various wavelengths (spectral bands) and making them into a single image. The MODIS Rapid Response System makes use of MODIS broad range of spectral observations by creating both true-color and false-color images, each tailored to highlight different land surface, atmospheric, and oceanic features. Some of the ways these bands can be combined are described below.
True-color
Long Answer True-color imagery uses MODIS Bands 1, 4, and 3, respectively corresponding to the red, green, and blue range of the light spectrum, are assigned to the red, green, and blue channels of a digital image. These images are called true-color or natural color because this combination of wavelengths is similar to what the human eye would see.	Short Answer Bands 1,4,3 (670 nm: 565 nm: 479 nm) Colors Fire detection=red outlines Advantages Natural-looking images of land surface, oceanic and atmospheric features.
Band 3,6,7 Combination
Long Answer The 3-6-7 composite assigns Bands 3, 6, and 7 to the red, green, and blue components of a digital image. This combination is good for revealing snow and ice because they are very reflective in the visible part of the spectrum, and very absorbent in Bands 6 and 7, which are a part of the spectrum called the short-wave infrared, or SWIR. Snow and Ice Since the only visible light used in these images (Band 3) is assigned to red, snow and ice appear bright red. The more ice, the stronger the absorption in the SWIR bands, and the more red the color. Thick ice and snow appear vivid red (or red-orange), while small ice crystals in high-level clouds will appear reddish-orange or peach. Vegetation Vegetation is absorbent in Band 3 and Band 7, but reflective in Band 6, and so will appear greenish in this band combination. Bare soil will appear bright cyan in the image since it much more reflective in Band 6 and Band 7 than Band 3. Water Liquid water on the ground will be very dark since it absorbs in the red and the SWIR, but small liquid water drops in clouds scatter light equally in both the visible and the SWIR, and will therefore appear white. Sediments in water appear dark red.	Short Answer Bands 3,6,7 (479 nm: 1,652 nm: 2,155 nm) Colors Vegetation=Green Ice or snow=Red Liquid water on the ground=Black or dark red Liquid water clouds=White Ice clouds=Peach Desert=Light blue-green Advantages Distinguishing liquid water from frozen water, for example, clouds over snow, ice cloud versus water cloud; or floods from dense vegetation.
Band 7-2-1 Combination
Long Answer In this composite, MODIS Bands 7, 2, and 1, are assigned to the red, green, and blue portions of the digital image. This combination is most useful for identifying burn scars. Vegetation and bare ground Vegetation is very reflective in the near infrared (Band 2), and absorbent in Band 1 and Band 7. Assigning that band to green means even the smallest hint of vegetation will appear bright green in the image. Naturally bare soil, like a desert, is reflective in all bands used in this image, but more so in the SWIR (Band 7, red) and so soils will often have a pinkish tinge. Burned areas If vegetation burns, bare soil in the area will become exposed. Band 1 slightly increases usually, but that may be offset by the presence of black carbon residue. The near infrared (Band 2) will become darker, and Band 7 becomes more reflective. When assigned to red in the image, Band 7 will show burn scars as deep or bright red, depending on the type of vegetation burned, the amount of residue, or the completeness of the burn. Water As with the 3-6-7 composite, water will appear black. Sediments in water appear dark blue.	Short Answer Bands 7,2,1 (2,155 nm: 876 nm: 670 nm) Colors Vegetation=Green Water=Black or dark blue Desert/Naturally bare soil=Sandy pink Burn scar=Red to reddish-brown, depending on the nature of the pre-fire vegetation and the severity of the burn. Advantages Distinguishing burn scars from naturally low vegetation or bare soil. Enhancing floods.

What do the orbit track maps show?

The maps have a series of white lines with tick marks on them that show what time (using Coordinated Universal Time, or UTC) the satellite will be passing over a particular location on Earth on a given day. The white lines represent the center of the swath. The time stamps mark the start of the northern (Terra) or southern (Aqua) edge of each 5-minute data collection period. An image acquired at that location will span roughly 1150 kilometers on either side of the tick mark. Every day there are two passes over most areas: one daylight pass, and one nighttime pass. At this point the MODIS Rapid Response System produces images for the daylight passes only.

At right, a cut-away from an orbit track map showing the Terra satellite overpass time near the Great Lakes (daytime granule starting at 17:10 UTC, nighttime granule starting at 03:35 UTC). Also marked is the location of the MODIS receiving station at the Department of Space Science and Engineering at the University of Wisconsin, which produces the maps.

Orbit track map with UTC time stamps in white

How can I tell when MODIS will capture an image of my area?

For Real Time Images

From the navigation bar at the top of all of our pages, Click the Real-Time button. Today's images will load with today's orbit track maps on the upper left side of the page.
If you know the latitude or longitude for your location of interest, you may use the Satellite Overpass Predictor on the Earth Observatory Web site to find out when Aqua MODIS or Terra MODIS will pass overhead. The satellite overpass predictor will also tell you the angle of the satellite to the location. Higher angles indicate that the location is close to the center of the image where details are clearer.
If you do not know the latitude and longitude of your area of interest, Click either the Terra or Aqua map.
The maps have a series of white lines with tick marks on them that show the time in Coordinated Universal Time (UTC) at which the satellite passes over that location. Find your area of interest, find the closest swath, and note the times of the nearest tick marks encompassing your area. (If you need help converting the UTC time stamp to your local time, visit TimeZoneConverter.com .)
- The image created at a particular time will encompass an equal area on either side of the line. Depending on how close the exact location you are interested in is to the actual orbital line (which represents the center of the swath), your image may be very sharp, if it is near the center, or degraded, if it is close to the edge.
- For every region there will be a daylight and nighttime pass. Only the daytime (i.e. local daytime) passes appear on our real-time production page.
- For more detailed orbit track maps, click on the links at the bottom of the maps.
Close the orbit map window and return to the thumbnail page. Thumbnails are labeled with a time stamp that is the start time of a five-minute data collection period or granule (its northern edge for Terra or southern edge for Aqua). They are arranged in chronological order.
Click on a thumbnail to see the image.
Use the previous and next buttons to see the images north and south of your image.
To find images from another day, Click on "Access other data from the archive" on the top right side of the page.
Select the day you want to view, and proceed as described above.

For Geometrically Corrected Images

The MODIS Rapid Response System produces daily geometrically corrected images of many regions of the world. These images are available in the subsets section of the site.

From the home page, click on the map on the right side of the page under "Near Real Time Subsets."
Click on the red square that covers your region of interest.
Use the previous and next buttons to move to images from the previous or next day, or select the day you want to view from the list of julian dates below the images.

Why do the real-time images look different from the gallery images?

Bow-tie effect

Satellite sensors collect data by pixels. A pixel of data represents the electromagnetic energy reflected from or radiated by a given area of ground. All these pixels are like individual boxes in a grid, and they are put together to make the complete image. In a single rotation of its scan mirror, MODIS captures an area on Earth about 2300 kilometers wide by 10 kilometers tall (imagine a long, thin rectangle). An image is put together by stitching one scan--one strip--on to the next.

Stretch
Because the area is so large, MODIS is looking straight down at the Earth in the center, but is looking off to the side at an angle. Just like the spot illuminated by a flashlight becomes wider the farther away the beam is pointed, the pixels that make up the MODIS image get wider the farther they are from the center of the image. Each MODIS scan gets stretched out at the edges, making the shape of each scan--each strip of the image--look more like a bow-tie than a true rectangle.

Overlap
Because the strips are wider at the edge than the center, the scans don't overlap in the center of the image, but they do overlap near the edges of the swath. This overlap creates a "double-vision" effect on the edges of the swath, as each point of the Earth's surface appears in two adjacent scans. This geometric distortion also makes the line where scans come together more pronounced, essentially magnifying tiny differences between one side of the scan mirror and the other, especially at the edge of the swath.

Distortion

The real-time images are displayed as they are scanned by MODIS, without correction for geometric distortion. Since the observed pixels at the edge of the swath are bigger than they are in the center, they appear to be scrunched into a too-small grid box when displayed "as-is" in the real-time imagery. We select certain images for geometric correction, and hand tailor them for our image gallery.

At right, matching images of Typhoon Rusa from the summer of 2002, showing the bow-tie effect (left) and geometric correction (right).

How do you correct for the bow-tie effect and distortion?

The code we use to correct for the bow-tie effect and distortion is not documented for distribution, but there are several free tools that will give similar results. We recommend the MODIS Swath to Grid Toolkit (MS2GT) or HDFLook.

Typhoon Rusa browse image, showing bow-tie distortion.

Typhoon Rusa with geometric correction for bow-tie effect

How do I make true-color MODIS images?

To help you create your own true color MODIS images, we provide a tutorial (pdf) that tells you where to get the software you need, including a version of our surface reflectance, fire detection, and vegetation index algorithms. Because of regulations on code distribution, code distribution is handled by the direct readout lab.

+ Download tutorial

I've tried making my own MODIS images from MOD09 data ordered from LAADS Web, but they don't look like yours. Why not?

We make our imagery directly from the MODIS L1B data (the calibrated, geolocated radiances), not the standard MODIS surface reflectance product (MOD09). Our images are based on custom surface reflectance code that has been developed with the specific aim of maintaining image integrity, as opposed to the standard MODIS surface reflectance product, which was developed with scientific integrity as the primary objective. For example, we do not use an atmospheric correction. In some cases, our images undergo additional hand-tweaking to enhance their appearance; for example, we apply a different color stretch to the land and ocean parts of an image.

Can you provide the full data file for an image I like in your gallery?

The MODIS Rapid Response System uses a subset of MODIS bands for generating imagery and identifying fire locations. We don't receive, and therefore cannot provide full spectral resolution data files (i.e., all 36 spectral bands). For recently acquired data appearing in the real-time part of our website, we include links to the full spectral resolution files (HDF files) that exist in an online data pool provided by the Level 1 and Atmosphere Archive and Distribution System (LAADS Web). This data pool supports a rolling archive of recent data. For more information on ordering MODIS data, see the MODIS website.

Can you send me geometrically corrected images and fire detections for my area of interest each day?

A substantial investment of time and resources is required to provide hand-tailored image processing for specific regions on a daily basis. The MODIS Rapid Response System provides these products daily to a small number of partner organizations, including the USDA Forest Service and Global Observation of Forest Cover partners. These images are available on the subsets page. As time and resources permit, we can occasionally respond to requests for coverage of significant events, and we are always interested in discussing the potential for meaningful scientific collaborations. If you are interested in proposing such a collaboration, please contact the MODIS Rapid Response Outreach Coordinator .

Do you produce fire detections at night?

Nighttime fire detections are currently being collected only for limited regions across the world but are not available via our website. In the future, we plan to add nighttime browse to our website.

What is the Julian day?

The Julian day, as we mean it, is the day of year (from 1 to 365 or 366). Most remote sensing data sets are identified using this julian date rather than the calendar date, because it is a more straightforward time scale for automatic processes. Note this is different from the common meaning of Julian Day as in Julian calendar. For conversions between julian date and calendar date, see this conversion table.

Where do you get the data used to draw political boundaries and coastlines on your gallery images?

This vector information comes from the National Geospatial-Intelligence Agency's (NGA) Vector Map (VMap) Level 0. It is available from the NGA website.

Where can I find the georeferencing information for your subset and gallery images?

The georeferencing information is contained in two places, the "More info" page and the JPEG World File. They are accessible from links in the upper left corner of each image page.

"More info" Page

This page describes the projection used to georeference the image, the latitude and longitude of the image center and corners, and some additional information about the image. If the image is rotated, the "rotation angle" field will be given. Counterclockwise rotation is positive; the image is first projected then rotated. If the pixel sizes are not equal in the X and Y direction. the "x scale factor" will be given; it can also be calculated: x_scale_factor = y_pixel_size / x_pixel_size.

Note that the coordinates given for the image corners are for the outside corner of the pixel, and thus will differ by one half of the pixel size from the numbers given in the JPEG World File.

JPEG World File

This file has the file extension .jgw and is an ASCII text file consisting of 6 lines, each containing a single number:

Value	Parameter	Description
250.000000000000	A	Pixel size in X direction
0.000000000000	D	Rotation term for Y
0.000000000000	B	Rotation term for X
-250.000000000000	E	Negative of pixel size in Y direction
-692125.000000000000	C	X location of center of upper left pixel
544375.000000000000	F	Y location of center of upper left pixel

The following equations will calculate the map coordinates of the center of pixel (x,y) when the coordinates of the upper left pixel are (0,0):

Map_X = Ax + By + C
Map_Y = Dx + Ey + F

Note that the pixel size in the Y direction is negative because the map origin is at the lower left and the image origin is at the upper left. The pixel size is in degrees for the Plate Carree projection and in meters for all other projections.

Some GIS and Image Processing software packages will not correctly handle images whose rotation terms (the second and third lines) are not 0.0.

How do I use your subset and gallery images in my GIS or Image Processing software package?

We are only able to do limited testing with subset and gallery images using GIS and Image Processing software packages and would greatly appreciate any questions, comments, corrections, clarifications, etc. on these instructions from our users. Please send them to the MODIS Rapid Response Outreach Coordinator.

NOTE that the global fire maps do not have georeferencing information.

NOTE on downloading the worldfile (it is a .jgw file) on Windows computers: Some versions of Windows append a ".txt" to the ".jgw" when you download it with "Save as type:" set to "Text Document." If the worldfile is saved with a ".txt" extension, the GIS program will not be able to find the worldfile. The name of the worldfile must match the name of the image file except with ".jgw" in place of ".jpg." To prevent this problem when downloading the worldfile in a Windows environment, change "Save as type": to "All Files". Also be aware that, when checking the worldfile name using Windows Explorer, in some versions you can't see the ".txt" if the "Hide extensions for known file types" box is checked in Folder Options. In this case, the file name looks correct when it is not.

ArcMap

To use subset and gallery images in ArcMap:

First download the image (it is a .jpg file) and the worldfile (it is a .jgw file)(if using Windows, see the note at the top of this FAQ). You will also need to have some of the information from the "More info" link handy. The "More info" link is above the image on the left.
Either before or after opening the image in ArcMap, you must set the Layer Coordinate System. The projection is specified by the "projection" in the "More info" page.
- Plate Carree
  - NOTE: Images in mid to high latitudes will appear wider than on our web site because our pixels are narrowed to approximate equal area while ArcMap forces the pixels to be square. (The "x scale factor" can be found in the "More info" page, the x_pixel_size is the first line of the .jgw file, the y_pixel_size is the fourth line of the .jgw file (with a "-" prepended) and x_scale_factor = y_pixel_size / x_pixel_size)
  - Right-click on "Layers", select "Properties..." then the "Coordinate System" tab
  - Select "Predefined" in the "Select a Coordinate System" box, then "Geographic Coordinate Systems" -> "World" -> WGS_1984
  - Click "OK" for "Data Frame Properties"
- Lambert Azimuthal
  - Right-click on "Layers", select "Properties..." then the "Coordinate System" tab
  - Select "<custom>" in the "Select a Coordinate System" box
  - Click the "New" button then select "Projected Coordinate System..."
  - Enter a name in the "Name" box
  - In the "Projection" panel, under "Name" select "Lambert_Azimutal_Equal_Area"
  - Set "False_Easting" and "False_Northing" to 0
  - Set "Central_Meridian" to the value from the "projection center lon" in the "More info" page
  - Set "Latitude_Of_Origin" to the value from the "projection center lat" in the "More info" page
  - In the "Linear Unit" panel, under "Name" select "Meter"
  - If if the value of "ellipsoid" is "WGS84" in the "More info" page, then in the "Geographic Coordinate System" panel, click the "Select" button, then "World" then "WGS84.prj" (Now skip to the "Click OK for New Projected Coordinate System" step)
  - If if the value of "ellipsoid" is "Sphere" in the "More info" page, then in the "Geographic Coordinate System" panel, click the "New..." button
  - Enter a name in the "Name" box
  - In the "Datum" panel, under "Name" select "<custom>"
  - In the "Spheroid" panel, under "Name" select "<custom>"
  - Set both "Semimajor Axis" and "Semiminor Axis" to the value from the "Earth radius (km)" in the "More info" page. You will need to move the decimal point 3 digits to the right to convert from kilometers to meters.
  - In the "Angular Units" panel, under "Name" select "Degree"
  - In the "Prime Meridian" panel, under "Name" select "Greenwich"
  - Click "OK" for "New Geographic Coordinate System"
  - Click "OK" for "New Projected Coordinate System"
  - Click "OK" for "Data Frame Properties"
- Sinusoidal
  - Right-click on "Layers", select "Properties..." then the "Coordinate System" tab
  - Select "<custom>" in the "Select a Coordinate System" box
  - Click the "New" button then select "Projected Coordinate System..."
  - Enter a name in the "Name" box
  - In the "Projection" panel, under "Name" select "Sinusoidal"
  - Set "False_Easting" and "False_Northing" to 0
  - Set "Central_Meridian" to the value from the "projection center lon" in the "More info" page
  - In the "Linear Unit" panel, under "Name" select "Meter"
  - If if the value of "ellipsoid" is "WGS84" in the "More info" page, then in the "Geographic Coordinate System" panel, click the "Select" button, then "World" then "WGS84.prj" (Now skip to the "Click OK for New Projected Coordinate System" step)
  - If if the value of "ellipsoid" is "Sphere" in the "More info" page, then in the "Geographic Coordinate System" panel, click the "New..." button
  - Enter a name in the "Name" box
  - In the "Datum" panel, under "Name" select "<custom>"
  - In the "Spheroid" panel, under "Name" select "<custom>"
  - Set both "Semimajor Axis" and "Semiminor Axis" to the value from the "Earth radius (km)" in the "More info" page. You will need to move the decimal point 3 digits to the right to convert from kilometers to meters.
  - In the "Angular Units" panel, under "Name" select "Degree"
  - In the "Prime Meridian" panel, under "Name" select "Greenwich"
  - Click "OK" for "New Geographic Coordinate System"
  - Click "OK" for "New Projected Coordinate System"
  - Click "OK" for "Data Frame Properties"

ArcView

NOTE: Some gallery images cannot be used in ArcView because they are rotated in order to capture more of the scene in a rectangular image. You can determine if an image is rotated or not by checking for the existance of the "rotation angle" keyword under the "More info" link for that image.

To use subset and unrotated gallery images in ArcView:

First download the image (it is a .jpg file) and the worldfile (it is a .jgw file)(if using Windows, see the note at the top of this FAQ). You will have to replace all the periods in the file names ("."), except the final one before the extension, with underscores ("_"). You can do this during the download process or afterwards. (Or you can completely rename the files, making sure that the portion before the .jpg and .jgw are identical.) You will also need to have some of the information from the "More info" link handy. The "More info" link is above the image on the left.
Make sure the ArcView JPEG Extension is enabled by going to File->Extension and checking "JPEG (JFIF) Image Support".
Either before or after opening the image in ArcView, you must set the View Projection. The projection is specified by the "projection" in the "More info" page.
- Plate Carree
  - NOTE: (1) The settings below will most likely be the default settings. (2) Images in mid to high latitudes will appear wider than on our web site because our pixels are narrowed to approximate equal area while ArcView forces the pixels to be square. (The "x scale factor" can be found in the "More info" page, the x_pixel_size is the first line of the .jgw file, the y_pixel_size is the fourth line of the .jgw file (with a "-" prepended) and x_scale_factor = y_pixel_size / x_pixel_size)
  - Go to View->Properties
  - Set "Map Units" to "decimal degrees"
  - Click the "Projection..." button
  - Click the "Standard" button
  - Set "Category" to "Projections of the World""
  - Set "Type" to "Geographic"
- Lambert Azimuthal
  - Go to View->Properties
  - Set "Map Units" to "meters"
  - Click the "Projection..." button
  - Click the "Custom" button
  - Set "Projection" to "Lambert Equal-Area Azimuthal"
  - "Spheroid" will be forced to a value of "Sphere"
  - Set "Central Meridian" to the value from the "projection center lon" in the "More info" page
  - Set "Reference Latitude" to the value from the "projection center lat" in the "More info" page
- Sinusoidal
  - Go to View->Properties
  - Set "Map Units" to "meters"
  - Click the "Projection..." button
  - Click the "Custom" button
  - Set "Projection" to "Sinusoidal"
  - "Spheroid" will be forced to a value of "Sphere"
  - Set "Central Meridian" to the value from the "projection center lon" in the "More info" page

ENVI

NOTE: Some gallery images cannot be used in ENVI because they are rotated in order to capture more of the scene in a rectangular image. You can determine if an image is rotated or not by checking for the existance of the "rotation angle" keyword under the "More info" link for that image.

To use subset and unrotated gallery images in ENVI:

First download the image (it is a .jpg file) and the worldfile (it is a .jgw file)(if using Windows, see the note at the top of this FAQ). You will also need to have some of the information from the "More info" link handy. The "More info" link is above the image on the left.
In order to save the new projections you will create, for projections other than Plate Carree, you will need to have a writeable copy of the file "map_proj.txt". First make a copy of the original ENVI file in your own directory space. (In our SGI installation, the file was found in the directory /usr/local/lib/idl_5.5/products/envi_3.5/map_proj) Second, you must make this copy of "map_proj.txt" your default copy by selecting File -> Preferences -> User Defined Files... and using "Choose" to select "Default Map Projection File". You must restart ENVI for the change to take effect.
Due to a bug (in some ENVI versions) in specifying some parameters for Lambert projections, you may need to create the projection in the "map_proj.txt" file. Instructions are provided below.
The projection is specified by the "projection" in the "More info" page.
- Plate Carree
  - NOTE: Pixels in images from mid to high latitudes will not be square in degrees because they are narrowed to approximate equal area. (The "x scale factor" can be found in the "More info" page, the x_pixel_size is the first line of the .jgw file, the y_pixel_size is the fourth line of the .jgw file (with a "-" prepended) and x_scale_factor = y_pixel_size / x_pixel_size)
  - Open the JPEG file with Open External File -> Generic Formats -> JPEG. Select the filename and click "OK"
  - The "JPEG World File Input Projection" dialog will appear.
  - In the "Select Input projection" box, select "Geographic Lat/Lon"
  - In the "Datum..." box, select "WGS-84"
  - In the "Units..." box, select "Degrees"
  - Click "OK" for "JPEG World File Input Projection"
- Lambert Azimuthal (using "map_proj.txt" file)
  - Edit your "map_proj.txt" file and add a new line containing the following:
  - A "36" for Lambert Azimuthal Equal Area (sphere), followed by a comma
  - The value from the "Earth radius (km)" in the "More info" page, followed by a comma. You will need to move the decimal point 3 digits to the right to convert from kilometers to meters.
  - The value from the "projection center lat" in the "More info" page, followed by a comma
  - The value from the "projection center lon" in the "More info" page, followed by a comma
  - Finally, "0.0,0.0," (for false easting and northing) followed by a unique name for the projection
  - Save the file with the new projection definition and restart ENVI for the change to take effect.
  - Open the JPEG file with Open External File -> Generic Formats -> JPEG. Select the filename and click "OK"
  - The "JPEG World File Input Projection" dialog will appear.
  - In the "Select Input projection" box, select the name of your new projection
  - In the "Datum..." box, select "<none>"
  - In the "Units..." box, select "Meters"
  - Click "OK" for "JPEG World File Input Projection"
- Lambert Azimuthal (using "Customized Map Projection Definition")
  - Open the JPEG file with Open External File -> Generic Formats -> JPEG. Select the filename and click "OK"
  - The "JPEG World File Input Projection" dialog will appear.
  - In the "Select Input projection" box, select "New..."
  - Enter a unique name in the "Projection Name" box
  - In the "Projection Type" box, select "Azimuthal Equal Area (sphere)"
  - Set "Sphere Radius" to the value from the "Earth radius (km)" in the "More info" page. You will need to move the decimal point 3 digits to the right to convert from kilometers to meters.
  - Set "False easting" and "False northing" to 0
  - Set "Latitude of projection origin" to the value from the "projection center lat" in the "More info" page
  - Set "Longitude of central meridian" to the value from the "projection center lon" in the "More info" page
  - Click "OK" for "Customized Map Projection Definition"
  - You will asked if you want to save the customized projection to the "map_proj.txt" and, if so, to select a filename and if you want to overwrite.
  - If you saved the projection, the next time you open the JPEG file, you can simply select the customized projection name from the "Select Input projection" box.
  - In the "Datum..." box, select "<none>"
  - In the "Units..." box, select "Meters"
  - Click "OK" for "JPEG World File Input Projection"
- Sinusoidal
  - Open the JPEG file with Open External File -> Generic Formats -> JPEG. Select the filename and click "OK"
  - The "JPEG World File Input Projection" dialog will appear.
  - In the "Select Input projection" box, select "New..."
  - Enter a unique name in the "Projection Name" box
  - In the "Projection Type" box, select "Sinusoidal"
  - Set "Sphere Radius" to the value from the "Earth radius (km)" in the "More info" page. You will need to move the decimal point 3 digits to the right to convert from kilometers to meters.
  - Set "False easting" and "False northing" to 0
  - Set "Longitude of central meridian" to the value from the "projection center lon" in the "More info" page
  - Click "OK" for "Customized Map Projection Definition"
  - You will asked if you want to save the customized projection to the "map_proj.txt" and, if so, to select a filename and if you want to overwrite.
  - If you saved the projection, the next time you open the JPEG file, you can simply select the customized projection name from the "Select Input projection" box.
  - In the "Datum..." box, select "<none>"
  - In the "Units..." box, select "Meters"
  - Click "OK" for "JPEG World File Input Projection"

How do I use the "Search by a keyword:" feature in your gallery?

Each Rapid Response Gallery image is annotated with keywords to aid in finding images of interest. The keywords fall into two categories, geographic, such as country, US state, Canadian province, and water body names, and image subject, such as "fire", "hurricane", "phytoplankton bloom", "volcano", "dust", "smoke", "iceberg", "snow", etc.

This is a very simple search which searches on a literal string. The search is not case sensitive and the string can contain blanks (e.g. "new mexico") or partial words. The search input can be multiple literal strings seperated by upper case "OR" (e.g., "hurricane OR typhoon OR tropical storm"). Similarly the search input can be a pair of strings separated by upper case "AND" (e.g., "canada AND fire"). The matching images are displayed with the most recent images at the top of the page. If no matches are found, only the search boxes will be displayed.

Some examples of keywords which will not work are city names and continent names. Continent names will return some images from that continent but it will not be a complete list.

How can I tell what time a subset image was acquired?

To find out when MODIS collected the data used in the subset image, click on “More Info” above the image. Under Level-2 granules, there is as list of the MODIS granules that are included in the image. The first two numbers in the granule name indicate the year; the next three numbers are the day of the year; and the final four numbers indicate the time of the overpass in UTC. For example, the file “A050351840” corresponds to the data collected on February 4, 2005, at 18:40 UTC. Click on the file name to see the real-time browse image for each granule.

The subset images may be composited from data collected in different MODIS overpasses at different times. Because the images cover set geographic regions, not a particular MODIS swath, the automated system that generates the subset images takes data from the overpasses that are closest to being directly overhead. Where overpasses overlap in the high latitudes of the north and the south, data from two or more overpasses (100 minutes apart) may be used to create the subset image. In these cases, a faint line may be visible where the two overpasses meet. White shows where data are not available either because MODIS has not imaged that region yet or because the area is out of the instrument’s range for that day. In equatorial regions, where overpasses do not overlap, MODIS data may not be available for the entire region every day. In these cases, a white wedge where no data were available may separate two MODIS overpasses.

How can I set up a direct broadcast system to receive data from the MODIS sensor?

The direct readout lab can provide more information about setting up a direct broadcast system. You can also find additional information on the MODIS home page.

How do I convert to NDVI values from the colors in your NDVI images?

The colors used for the ndvi subset images (since June 2, 2004 (2004154), except NewMexico) can only be converted back to one-tenth NDVI ranges, as follows:

Color NDVI

R G B

153 204 255 <=0.0

225 175 100 0.0-0.1

255 225 150 0.1-0.2

225 255 175 0.2-0.3

152 255 152 0.3-0.4

102 255 102 0.4-0.5

51 204 51 0.5-0.6

0 153 0 0.6-0.7

0 102 0 >0.7

255 255 255 no data

Click here for the conversion table for realtime images, subset images before June 2, 2004 (2004154), and the NewMexico subset.

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