A DTM (or synonymously DEM for Digital Elevation Model) is a grid, or raster, file describing elevation values at regularly spaced points, or posts.

HiRISE DTMs are made from two images of the same area on the ground, taken from different look angles. All the stereo pairs acquired so far are available here. Not all of these have been made into DTMs due to the time-intensive process. Creating a DTM is complicated and involves sophisticated software and a lot of time, both computing time and man-hours.

As mentioned in a previous post, the great advantage of a HiRISE DTM is the high resolution of the source imagery. As a general guide, terrain can be derived at a post spacing about 4X the pixel scale of the input imagery. HiRISE images are usually 0.25 – 0.5 m/pixel, so the post spacing is 1-2 m with vertical precision in the tens of centimeters.

The three basic stages of creating a DTM are:

1. Prepare the images for ingestion into the stereo software
2. Triangulate the images
3. Extract terrain

In order to prepare the images, we must first correct the geometry by removing any optical distortions inherent to HiRISE. Then the spacecraft pointing information at the time of each observation is gathered.

Triangulation is also called bundle adjustment. This step requires the most operator skill and time. The result is a transformation of the original images to epipolar space. What this means is that all the stereo information is now captured in the horizontal direction, or x-parallax. During triangulation, we also align the stereo model to MOLA elevations, so the end result is tied to the global elevation map produced by the MOLA instrument team. This is the same map that you see in the context map pane of every HiRISE observation page.

Once the images are triangulated, then terrain can be extracted. This step is computationally intensive, but automated, so it just takes a lot of computer time. The output of terrain extraction is reviewed for any artifacts or errors. These are edited out if possible. Since editing is extremely time-consuming, it is only done on easily corrected errors and in the areas of most interest to the researcher. The less editing we have to do, the better, so a lot of effort goes into preparing the images so that the input is as high quality as possible. The excellent contrast and value range of HiRISE imagery usually result in high quality terrain extraction that requires minimal editing.

After we have terrain, we can make other products, such as orthoimages. An orthoimage is a picture that has been orthorectified. This means that the pixels have been projected so that at each pixel it is as if you are looking directly down at the terrain. In the original stereo images, we rely on the fact that there are topographical distortions (parallax) to derive the elevations in the terrain model. In the orthoimages, all topographic distortions have been removed.

The final products are map projected using the same mapping definitions as the regular HiRISE RDR products.

A really useful (and cool) thing to do with the orthoimages is to drape them over the terrain for 3D viewing. Below is a subimage from the Newton Gullies DTM showing the imagery draped over the terrain.

You can see animated fly-throughs made with HiRISE DTMs by going to the HiClips page and clicking on the JPL Flythrough Clips. This is a great way to see and understand the geological relationships from a ground perspective.

Researchers use DTMs to take measurements and model geological processes. DTMs are very powerful research tools. In fact, almost every HiRISE DTM produced results in publication. There is a long waiting list for these products because they are so valuable and so difficult to produce. Several institutions involved with HiRISE contribute to DTM production to maximize the number of projects produced and to avoid duplication of effort.

Standard PDS products linked to the DTM project page are usually quite large files. The links provided will download the files to your system. To get a quick view of what the project looks like, click on the Extras links to see a reduced version of the products, displayed as images, grayscale, shaded relief and colorized altimetry.

Standard PDS products:

• The DTM in standard PDS image object (.IMG) format with an embedded label
• The left orthoimage at the same resolution as the DTM, in JPEG2000 format with detached label
• The left orthoimage at the resolution of the original image, in JPEG2000 format with detached label
• The right orthoimage at the same resolution as the DTM, in JPEG2000 format with detached label
• The right orthoimage at the resolution of the original image, in JPEG2000 format with detached label

Extras available in the PDS Extras directory (letters in parentheses correspond to PDS file names such as <Product_ID>.br.jpg):

• Browse (br), annotated browse (ab), and thumbnail (th) jpegs of the DTM as a grayscale image
• Browse (sb), annotated browse (sa), and thumbnail (st) jpegs of the DTM as a shaded relief image
• Browse (cb), annotated browse (ca), and thumbnail (ct) jpegs of the DTM as colorized altimetry
• Browse (br), annotated browse (ab), and thumbnail (th) jpegs of the lower resolution orthoimages

PDS product naming convention for HiRISE DTMs:

PRODUCT_ID = aabcd_xxxxxx_xxxx_yyyyyy_yyyy_Vnn
where
aa = DT, indicating it’s a DTM product
b = type of data

• E = areoid elevations
• 1 = orthoimage pixels from first image
• 2 = orthoimage pixels from second image

c = projection (others are possible but these are the important ones)

• E = Equirectangular
• P = Polar Stereographic

d = grid spacing (think of this as pixel scale in meters)

• A = 0.25 m
• B = 0.5 m
• C = 1.0 m
• D=2.0 m

xxxxxx_xxxx = orbit number and latitude bin from SOURCE_PRODUCT_ID[1]
yyyyyy_yyyy = orbit number and latitude bin from SOURCE_PRODUCT_ID[2]
V = letter indicating producing institution

• U = USGS
• A = University of Arizona
• C = CalTech
• N = NASA Ames
• J = JPL
• O = Ohio State
• Z = other

nn= 2 digit version number

Below is an example of the set of annotated browse images for the Russell Crater Dunes DTM.

The grayscale image of the DTM looks weird, if you have not looked at lots of these before, but keep in mind that the color of the pixels represents elevation. The higher the elevation, the brighter the pixel. Lower elevations are darker. The shaded relief is another way of visualizing the topography. The pixels are illuminated from a certain direction, to show the relief of the topography, rather than the elevation. It is also emphasizes any artifacts in the DTM. In the example here, many artifacts (errors) can be seen such as the faceted areas and boxes in the lower left and top of the image. These artifacts are usually caused by areas of low contrast (such as in this project) or sharply differing shadows. Most HiRISE DTMs will not have a lot of these artifacts, fortunately! The area of most interest to the researcher who requested this DTM was the long slope with the gullies, which was well-illuminated and had good contrast. So in that area, there were few, if any, artifacts. Adding color-coded elevation to the shaded relief creates the colorized altimetry map, where the lowest elevations are purple, green is the median elevation value, and white is the highest elevation. In the Russell Crater Dunes project shown here, the difference in elevation from the highest to the lowest point is almost 590 meters (~1935 ft.). That is a tall dune!!

We are happy to be able to share HiRISE DTMs with the scientific community and with the public. We will continue to release more DTMs as they become available, so stay posted!

You might remember that we were planning on releasing HiRISE images to the public on a monthly basis. That plan was delayed by issues with our processing software, hardware and other events. A productive summer working on these issues culminated last week with one of our larger releases of Mars images!  Here are some statistics about our September 2009 release, which includes the images the HiRISE camera took of the Martian surface between Mars Reconnaissance Orbiter (MRO) orbits 12,600 to 14,199, or roughly April 4 through August 6, 2009:

• 2,996 RDRs, 1 TB
• 42,370 EDRs, 1 TB
• 34,481 RDR Extras, 1.6 TB
• 83,784 EDR Extras, 0.02 TB
• 636 Anaglyphs, 0.01 TB

Totals for this release: 163,631 image products, 3.6 TB

This brings our total released product numbers and data volume to:

• 22,676 RDRs, 12 TB
• 317,120 EDRs, 10.4 TB
• 192,270 RDR Extras, 15.3 TB
• 612,769 EDR Extras, 0.1 TB
• 2,892 Anaglyphs, 0.5 TB

Total: 1,148,363 images, 37.5 TB

In summary, we released nearly 1500 observations, most of those with both black & white and color RDR products. Several newer observations matched up with older observations from a slightly different angle of the same location on the surface, resulting in 636 awesome new anaglyphs. The RDRs are the fully processed, geometrically projected products best for scientific inquiry. If you really want to, though, anyone can download and process HiRISE data from scratch. You can do this using ISIS software, which is publicly available for free download. See the ISIS Web site for download information, processing instructions, and tutorials.

Starting this week, I will be looking over the observations taken August 6 through August 26 before MRO went into safe mode and make sure they are ready for release. We plan to release these images in early October. We are also in the process of reprocessing those Extended Science Phase mission images prior to all the latest processing pipeline fixes and updates.  Once we are satisfied with that data set, we will release them to the public and then start reprocessing the images from the Primary Science Phase…a major project that should keep me and the rest of Downlink busy for several months!

It’s summer again in the southern hemisphere of Mars, so we’re continuing our mosaic of the landing ellipse for the lost Mars Polar Lander. ESP_013368_1035 was the first of the new images to be released, and we’ve gotten a lot of people asking where to send their candidates. You can either contact us directly, or add to the comments in our previous blog post about the search.

The Unmanned Spaceflight forums have a long discussion on the previous search efforts. Many candidates were proposed, and the community’s discussion about them is quite enlightening.

Emily Lakdawalla at the Planetary Society also started a coordinated search effort last year. I don’t know if that effort is still ongoing, but her page on how to use HiRISE images in the search is still a great resource. It includes examples of known hardware, cosmic ray hits and other artifacts, and more tips on searching.

In addition to the list of images on the previous blog entry, these new images have been released: (we’ll try to keep this list up to date as more are released)

• ESP_013368_1035
• ESP_013078_1030
• ESP_013223_1025
• ESP_013289_1035
• ESP_013566_1025
• ESP_013500_1035
• ESP_013711_1030
• ESP_013724_1030
• ESP_013935_1030
• ESP_013790_1035
• ESP_014001_1040
• ESP_014080_1040

Thanks for all your interest, and good luck searching!

9/2/09: ETA new images released in September PDS release.

Planetary scientists used to keep new data from the spacecraft explorers of the solar system within the mission team for a lengthy period of time so they could make all the cool initial discoveries. Only later would the mission’s data sets be archived on the public Planetary Data System (PDS). Once archived, these data could then be used by the scientific community and public for further research and discovery.

Dr. Alfred McEwen, HiRISE principal investigator, decided early on that this incredibly powerful instrument should be “The People’s Camera”. This meant, among other things, that we would endeavor to make the data returned by HiRISE available to the scientific community and public as quickly as possible. We have PDS release requirements, but our goal has always been to beat those requirements. To do so, we needed to develop automated software pipelines to take the raw data and turn them into useful calibrated and geometrically mapped products. We also needed to develop the right PDS release tools, train a talented group of operations staff to validate the data and fix problems, and develop a website to effectively and beautifully showcase HiRISE images.

We now believe we have reached the point to be able to support a monthly release of recent HiRISE images to the public! This week we released the observations HiRISE took of Mars between orbits 11,600 and 12,599, or between January 16 and April 04, 2009. This makes us the first mission to release a data set to the PDS so quickly! Here are the statistics for this release, including the number of each product type released and their respective data volumes (EDRs are the individual uncalibrated image channels and RDRs are the calibrated, mosaicked, and geometrically-projected observations):

• 1,179 RDRs, 520 GB
• 16,861 EDRs, 459 GB
• 13,512 RDR Extras, 788 GB
• 33,152 EDR Extras, 7 GB
• 342 Anaglyphs, 51 GB

Totals for this release: 64,704 image products, 1.7 TB

This brings our total released product numbers and data volume to:

• 19,667 RDRs, 11 TB
• 278,807 EDRs, 9.5 TB
• 166,816 RDR Extras, 13.7 TB
• 529,095 EDR Extras, 0.1 TB
• 2,892 Anaglyphs, 0.5 TB

Total: 993,277 images, 34 TB

Those are various products for about 9998 Mars observations, and another reason why it makes no sense to hoard our data; there is too much of it and too few of us! The team scientists have plenty to do and there are plenty of discoveries to be made, old hypotheses to update, and new mysteries to solve.  The operations staff are now hard at work getting observations from orbits 12,600 through 12,999, or between April 04 and May 5, 2009, ready for the June PDS release. This involves making sure each observation has been processed by our software pipelines correctly, fixing any problems, and checking and double checking that the relevant image products are ready for release.  Sometimes we have to manually force an observation through the pipelines because some of its channels were lost during transmission to the Earth, or we might stumble across an observation we somehow forgot to send on to the color pipelines after it had been calibrated. There are spreadsheets to maintain, lists of problematic observations to keep (see the ERRATA.TXT file), and a variety of other tasks that need to be completed before the latest data set is ready for release.

Over the next few months we will see how this goes! It is a lot of work, but our desire for you to see these beautiful images of Mars as quickly as possible is strong. No promises, but we will also explore releasing completed observations even faster!

New feature on the HiRISE website! HiFlyers made of released images like this one:

These are 11×17 PDFs showing cutouts of new releases, so you can print your own posters. Currently these are available for weekly releases starting 3/25/09 – look for more with each week’s new images!

They’re all available on this page. There are also links to the flyers on the individual image pages such as this one: http://hirise.lpl.arizona.edu/ESP_011425_1775 (Look for the “HiFLYER” link in the lower right hand side.)

Enjoy!

One of our blog readers asked about the wallpapers we post on our website for some of our released images. If you haven’t seen these, they’re linked over on the lower right of pages like this. Many different sizes are available, from 800×600 all the way up to 2560×1600 (for lucky people with ginormous monitors), so you can choose the right size for your screen resolution.

Our masterful web master creates these wallpapers for each of our weekly captioned releases (these are the images we release each week with some commentary written by the science team). He picks out an interesting area from each image and produces custom cutouts in different sizes. We provide these extra files because we think the images are so beautiful, everyone should have them on their desktop. Because they’re all done by hand, though, we unfortunately don’t have the resources to make these special products for every single image. For example, most of the 1,642 images we released in our big December PDS release don’t have wallpapers. However, you can make your own, and here’s how!
(more…)

After the long process of creating the HiGlyph Pipeline (anaglyphs producing software), processing the images through this pipeline and having them all properly validated, we here at HiRISE are proud to present you with a whole mess of anaglyphs (362 of them, to be exact )!

And now, for all of those curious minds out there, a brief overview of the HiGlyph Pipeline:

• Anaglyphs are created in a three-step process. The first step is to take the two images of the stereo pair and map project them. This helps the pipeline determine which image will be the left image and which will be the right image in the anaglyph.

• The second step takes the two images and looks to see if there are any improvements that can be done on them before putting them together. If there are not, the images move on. Often, due to the difference in viewing angle, the two images do not have a 100% overlap. Thus, to make the image a bit neater and easier to see, we trim off the excess portion of the image (the parts that do not overlap) and then assemble them so the left image is the red and the right image is the blue/green.

• The third and final step of this image processing is simply to prepare the images you see here and to update our catalog.

Seems complicated, right? Well luckily we have wonderful programmers that create these intricate programs. All I have to do is create a list of these images and run them through this pipeline. What really makes my job interesting is the validation process!

I have had the pleasure of being able to look at all 362 of the anaglyphs we have released today. But, you might ask, aside from looking super cool in 3-D glasses , what does it take to validate these anaglyphs? Well, at the beginning of this process the student validators and I got to ask that very same question. Since HiRISE has never had software to create images like this before, we played lab rat and came up with an entirely new technique for validation.

• You may notice that when not wearing the 3-D glasses there is a bit of a horizontal shift in the anaglyph. This shift is good because it is what allows us to see the image in 3-D. But, since the map projection of this process is not always spot on, we sometimes wind up with a vertical shift too. This is bad! Since most of us do not have googly eyes, this makes the image very difficult to see. With our validation process, we have to spot this out and fix it so that you do not have to strain your eyes (well… not too much at least ) in order to see the anaglyph.

Well, with that said, I leave you to your regularly scheduled HiRISE browsing! Enjoy!

We’re going to release a bunch of anaglyphs next week! The ones I’ve seen are really cool. Personally, I have to work a little on focusing my eyes to make them look right (maybe I need new glasses!), but it’s totally worth it. The landscape pops right out of the screen, showing intricate textures in so much detail it’s almost tactile. Sometimes I want to reach out and touch my computer screen to feel the depths of valleys, individual boulders, and folds in the layering.

Here’s the teaser, including a link to where to get your own 3-D glasses. Here’s another blog entry explaining how we take the stereo images that are used to create the anaglyphs: Hi-Fi Stereo (the other kind) The new anaglyphs we’re releasing will be processed differently (I’m not sure of the details, but hopefully we’ll get someone who better understands the processing to explain it). Instead of the magenta tint of the previous analgyphs we had made by hand (like this example to the left), they will just be regular gray-scale, which I think is less distracting.

Here are a few excerpts from yesterday’s University of Arizona story about our PDS release:

The HiRISE team has so far released a total 26.9 terabytes of data…. That amounts to more data than has been released by all previous deep space missions combined.

“If I showed each HiRISE image for 10 seconds, it would take me about 4 years to show them all,” said UA’s Alfred McEwen, HiRISE principal investigator.

…

Spacecraft motion pushes this electronic array so that it records the view down to Mars’ surface at a ground speed of about 3.2 kilometers per second, or about 7,000 miles per hour.

Skeptics doubted that a technique called “time integration delay,” needed to compensate for extremely short exposure times – about one ten-thousandth of a second per pixel – could produce sharp, unsmeared images.

But the technique has worked “wonderfully well,” thanks to accurate spacecraft pointing and stability and precise exposure time calculations, McEwen said.

Click here for full story.

We’ve just released 1008 new HiRISE images to the PDS! (See main page, or click here for the catalog.) This release covers orbits 8200 – 9299 of the primary mission, or in other words, the end of April through the end of July. That means we’re releasing data that’s only about 6 weeks old! This is awesome – I’m so impressed with the downlink team! The amount of work required to process these images is astounding, let alone prepare and post everything for an official release.

Here are a few examples of cool images, which were previously unreleased:

• PSP_008248_2640, Polygons and spots on defrosting dunes (right)
• PSP_008269_1395, crazy weird stuff in Hellas Planitia (be sure to look at the whole browse image on this one!)
• PSP_008322_1865, Multiple generations of slope streaks on a crater in Arabia Terra (left)
• PSP_008343_1430, Gullies on mesas in Gorgonum Chaos

I’ve only looked through the first few pages in the release. I know there are a lot more amazing images in there, so if you’re browsing through the images, post some of your favorites below!