Finding THEMIS Images with the Web Map
The web map lets you find THEMIS images for areas on Mars just by pointing and clicking.

In essence, the process works as follows. Begin by zeroing in on a particular feature or area using the map. Then use filters to identify images available for that location. Finally, open the images and download them.

Each map element (Operators, Filters, etc.) has a specific function, described below.

At the end of this guide are some useful hints and suggestions.

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Quick Help
quickhelp
Clicking this icon pops up a highly condensed guide to finding THEMIS images, aimed at first-time users.

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Operators
Operator buttons control what a mouse click on the map does.
zi
After you click the Zoom In operator button, a mouse click on the map recenters the map on that point and zooms in by a factor of about 2. You can zoom in repeatedly. Distortion will occur in some areas, because the map is a simple cylindrical projection.
zo
After you click the Zoom Out operator button, a mouse click on the map recenters the map on the point and zooms out by a factor of 2. You can repeat this until the whole map is visible.
pan
After you click the Pan operator button, a mouse click on the map recenters the map on that point without changing the magnification.
select
After you click the Select operator button, a mouse click anywhere on the map looks for a THEMIS image covering that point. If any exist, a link for each image appears in both the Thumbnail frame and the Image List. Click either the thumbnail or the reference number to open a new browser window with details of that image and downloading options.
link
Clicking the Link to this Page operator button creates a link in your browser's address window that captures the current filters, map background, zoom-in state and chosen images. If you save the link as a Bookmark or a Favorite, you can return to that point at any time.
help
Clicking the Help operator button opens this user guide.

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Position
pos

The position display gives the martian latitude and longitude of the mouse point in degrees and decimals of a degree. Latitude is given first and runs from 90° north to 90° south. Longitude increases eastward from 0° to 360°, measuring from the central meridian.

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Filters

You can search for THEMIS images by choosing among three filters: Release, Time of Day, Camera. The three filters work together as a sieve: each filter limits the results of the other two.
Release

The THEMIS project began releasing data to the public every three months beginning in October 2002. All releases are grouped together by the mission year* in which the data were collected. A year on Mars lasts roughly 687 days. The latest release, dated in the form of month/year, is also presented separately. (When the map loads, a release has been chosen.) Selecting a different release updates the map, showing the images from only that release.

* This year count started when the spacecraft (Mars Odyssey, or MO) arrived. For the purpose of long-term observations, however, scientists also have a chronological Mars year count, which began April 11, 1955. In this chronological system, MO year 1 for THEMIS occurs at the end of Mars year 25.

release
Choosing all releases redraws the map to show the footprints of all images that meet the chosen Time of Day and Camera filters (see below).

Choosing daily images retrieves the footprints of all Images of the Day that meet the chosen Time of Day and Camera filters.

Choosing no releases clears the map.

Time of Day

Choosing a Time of Day filter refreshes the map and shows the footprints of images selected by that filter.
tod
Choosing daytime shows only images taken in daytime. Footprints of daytime images (visible or infrared) tilt toward the right. Daytime is the default choice when the map loads.
tod
tod
Choosing nighttime shows only nighttime images. Footprints of nighttime images tilt toward the left.
tod
tod
Choosing day + night shows both.
tod
tod
Choosing none clears the map.
tod
Camera
Choosing a Camera filter refreshes the map and shows the footprints of images selected by that filter.
tod
Choosing visible shows the footprints of visible wavelength THEMIS images. Visible image footprints are depicted in blue.
tod
Choosing infrared displays the footprints of infrared THEMIS images. Infrared images have footprints in red.
tod
Choosing vis + ir displays both. This is the default choice when the map loads.
tod
Choosing none clears the map.

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Background
All Background maps are simple cylindrical projections and have a resolution of roughly 64 pixels per degree, or about 1 kilometer (half a mile) per pixel. The projection becomes increasingly distorted toward the poles.
bg
Choosing albedo displays a grayscale surface map derived from Viking Orbiter data. At right is an albedo thumbnail of the Valles Marineris region.
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Choosing shaded relief displays a grayscale shaded-relief map created from Mars Orbiter Laser Altimeter (MOLA) topographic data. At right is a shaded-relief thumbnail of the Valles Marineris region.
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Choosing mola displays a vividly colored shaded-relief map derived from Mars Orbiter Laser Altimeter (MOLA) topographic data and United States Geological Survey (USGS) digital maps. At right is a mola thumbnail of the Valles Marineris region. The mola background is the default choice when the map loads.
bg
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Choosing mola 2 displays a traditionally colored shaded-relief map derived from Mars Orbiter Laser Altimeter (MOLA) topographic data and United States Geological Survey (USGS) digital maps. At right is a mola 2 thumbnail of the Valles Marineris region.
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Map
What you see on the map reflects your current choices of filters and background.
map
In this example, the user chose daytime infrared, nighttime infrared, and visible wavelength images on a grayscale shaded-relief background.
map
In this example, the user chose daytime infrared images and the mola 2 color shaded-relief map.

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Image List
The Image List gives the reference numbers of any THEMIS image footprints that cover the map spot the mouse clicked on (in Select Mode).
il
In the example at left, four infrared (I) and two visible (V) wavelength images were found. Clicking the I02152002 link would pop open a window providing detailed information about the image and choices of image formats for downloading.

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Thumbnails
When you choose the Select operator (see above) and click on the map, the Thumbnails frame shows small versions of any THEMIS images covering the spot the mouse clicked on.
tnails
In this example, one infrared and one visible wavelength image were found. Clicking any thumbnail pops open a window giving detailed information about the image and choices of image formats for downloading.
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Some hints and suggestions
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