India Launches World's First Stereo Imaging Satellite

sgups writes "India will tomorrow inaugurate a new launch pad at its Satish Dhawan space port near Chennai, on the south-east coast, by putting the world's first stereographic mapping satellite into orbit. The most innovative feature of the 1.6-tonne Cartosat-1 is its pair of cameras, which will give stereo images of the earth's surface that can distinguish features down to 2.5 metres across. They will directly generate three-dimensional maps that have until now been achievable only indirectly, by combining data from a large number of satellite passes over the same place. "Such a stereographic imaging system does not exist in the civil sector anywhere else," says Mr Nair, chairman of the Bangalore-based Indian Space Research Organisation (Isro). "It will give information about heights that will be very useful in applications such as planning power lines." Cartosat-1 will join what is already the world's largest cluster of non-military remote sensing satellites. Six Indian spacecraft are already observing the earth with a wide range of instruments."

NRO

[swb]

...probably had this ability in the late 60s or early 70s.

Re:How many military satellites already do this?

[Wyatt Earp]

Weather Radar on birds with ISAR can do this.

http://www.madsci.org/posts/archives/2004-09/10940 49193.Ph.r.html [madsci.org]

I've exchanged email with NOAA about hurricane photos and have been told that some of them are inface ISAR radar images that have been colored.

The blurb there for the story sounds like a Press Release there from Mr Nair, chairman of the Bangalore-based Indian Space Research Organisation (Isro).

Re:NRO

[dschuetz]

...probably had this ability in the late 60s or early 70s.

Check out the cameras [nro.gov]

Don't know when the birds got stereo capability, but the first photos were returned in 1960 [nro.gov].

Camera motion used to generate stereo pairs

[Critter92]

Due to spacecraft (or aircraft) motion, stereo pairs are generated along the flightpath if sequential images overlap. In many systems, each image n generates overlap with both image n+1 and n+2. Given the ability to launch two cameras, why not launch a single camera with more capabilities? Another minor, and common, error is that the Cartosat-1 has a 2.5m pixel on its CCD, which does not transalate into a 2.5m "resolution." CCD resolution corresponds to Ground Sampled Distance (GSD), or the amount of ground sampled on one pixel. Ground resolved distance, (GRD), measures the highest frequency visible in the image and is what we normally think of as "resolution." As a result, for electro optical systems, GRD = 2 x GSD.

Re:Not the distance between the cameras

[starfishsystems]

This is just supposition, based on the fact that two cameras on a satellite would not be far enough apart to generate parallax.

Makes sense, though. According to the article, the orbit is at 620km. To obtain 1.0 degrees of stereo separation would require cameras placed 10.8km apart.

Re:What? How far apart...

[TripMaster Monkey]

Perhaps you ought to RTFA (or at least TFS)...

The most innovative feature of the 1.6-tonne Cartosat-1 is its pair of cameras, which will give stereo images of the earth's surface that can distinguish features down to 2.5 metres across. They will directly generate three-dimensional maps that have until now been achievable only indirectly, by combining data from a large number of satellite passes over the same place.

Largest Cluster of RS satellites?

[cerulean_blue99]

Perhaps I'm not understanding how the submitter is using the term "non-military", and not to wave Uncle Sam's flag too much, but offhand I can think of more than six US RS platforms/sensors:

EOS/Terra/MODIS http://modis.gsfc.nasa.gov/ [nasa.gov]
Landsat ETM+ http://landsat.gsfc.nasa.gov/ [nasa.gov]
Landsat MSS (yes still going)
AVHRR http://daac.gsfc.nasa.gov/data/dataset/AVHRR/ [nasa.gov]
GOES http://www.goes.noaa.gov/ [noaa.gov]
ASTER http://asterweb.jpl.nasa.gov/ [nasa.gov]

Not to mention US based commercial satellites:

IKONOS http://www.spaceimaging.com/ [spaceimaging.com]
Quickbird URL:http://www.digitalglobe.com/

Re:Need clarification

[CrackedButter]

There is no such thing as 1st, 2nd and 3rd world nations any more. There are only developed and developing nations, India being of the developing kind.

Re:What? How far apart...

[ravind]

From the document:

The spacecraft is configured with the Panchromatic cameras which are mounted such that one camera is looking at +26 deg. w.r.t. nadir and the other at -5 deg. w.r.t. nadir along the track. These two cameras combinedly provide stereoscopic image pairs in the same pass.

No

[briancnorton]

GPS altitude is not very accurate, (could easily be off by 10+ meters) but that's not the point. If you need to get accurate relative elevations, you need stereo or radar/lidar. Stereo is VERY accurate, but very labor intensive and you get elevations off the tops of trees, not the ground. (makes a big difference when putting up a power line) Radar penetrates, but is very expensive and technically sophisticated to build and process, and you can end up with a LOT of wierd artifacts. LIDAR is VERY ACCURATE, but you still get treetops rather than ground, and it's TRES EXPENSIVE, more suited to a small area than a huge country.

I have something of a hard time seeing the utility of this new system.

Re:Need clarification

[groovy.ambuj]

India has been doing VERY good in applied sciences and technology in spite of limited resrouces.. mainly because of huge techi population. Its one of the 5 nations to launch PSLV, is working on intercontinetal ballistic missles, one of 5-6 nuclear nations. So, as far as space research is concerned i wouldn't call it 3rd world country :-) And, at least in space research, there is virutally no coperation between US and India after Indian nuclear test in 1998.

Not first stereographic, but first hi-res stereo

[Dominic_Mazzoni]

This isn't the first stereographic satellite that's accessible to the general public; that would be MISR [nasa.gov] - NASA's Multi-angle Imaging Spectroradiometer, built by JPL, with nine cameras pointed in different directions along its direction of travel in polar orbit, ranging from nadir (straight down) to 70 degrees in either direction. Compared to India's new high-resolution satellite, MISR seems very low resolution - 275 meters per pixel - however, it covers the entire surface of the Earth every few days and all of the data is available for free at this resolution, while India's satellite is "targeting"; it only images a particular area when it is programmed to do so. MISR is used primarily to study clouds and aerosols.

To see some 3-D images taken by MISR or some animations of its 9 cameras' views of different scenes, check out their gallery [nasa.gov].

Re:Parallax by pointing

[robslimo]

Thanks. It seems you're right. It was in there in the specs I linked, but they didn't come right out and say it. Had a little trouble wrapping my mind around it, but it makes good sense.

Re:Imagine the Possibilities

[nagudaku]

some technical details on the ISRO website: http://www.isro.org/Cartosat/Page3.htm [isro.org]

Re:question for anyone

[Anonymous Coward]

Do a Google search for Hipparcos, sometimes spelled Hiparcos. It's an ESA mission that's been taking high quality parallax data of hundreds of the nearest stars, for something like a decade now. Before that, Earth-based observers have been able to measure parallax to even closer stars. These distances are the most accurate measured in astronomy, and are used to calibrate distance scales based on other phenomena, like variable stars. The data, like many scientific endeavours, is publicly available, although you'd probably be hard pressed to do anything interesting with it. There are a number of programs available that let you visualize the local 3D starfield, if that's your interest.

Re:All this...

[brontus3927]

If they spent their entire GDP on literacy, housing, healthcare, etc so that every Indian citizen would read, write, have a place to live, and food to eat, they wouldn't have any money for technological programs. At that point, people would lament how "backwards" the country was because it was existing largely on 19th century technology.

India has a population of 1,065,070,607 [google.com] whereas the US has a poulation of 293,027,571 [google.com]

52% of 1,065,070,607 is 553,836,715 and 97% of 293,027,571 is 284,236,743. That means India already has 269,599,972 more literate people than the US

Re:All this...

[Telastyn]

Where'd you get those numbers?

Google shows their budget to be somewhere around $3.3 billion US over 5 years or about $650m.

Given nasa's budget of $16 billion US, and the US's population of 300m, per capita income of $30k VS india's 1b population at $3k per capita...

The amount of tax [compared to per capita income] needed to fund the space programs are nearly identical. (around .0002% of their yearly income if my math is correct)

Re:Big problem

[gabe824]

The stereo pair is not collected at the same moment. One image will be collect with a camera looking forward a few degrees and then once the satellite has pasted over the target, a second image will be taken looking back with the second camera. This technique is along-track stereo and has been used before. Cross-track stereo has also been used where an image will taken looking off to one side and then the second image will be taken on a subsequent orbit looking off to the other side. Along-track stereo has a big advantage in that the two images are taken within seconds of each other and will therefore have similar atmospheric and lighting conditions which improves analysis.

Re:Why two cameras needed?

[Jerf]

Langolier posted the correct answer [slashdot.org] with info not available in the FA.

Everyone who posted before this is encouraged to be a little more careful providing answers in the future. (All four that I can see are not only wrong, in the sense they don't contain the correct explanation, but also in the sense that they contain serious technical errors.)

RE: Why 2 Cameras/paralax?

[Anonymous Coward]

Ok, For those of you wondering why they use 2 cameras . . . Don't think of it as a typical camera CCD sensor, where you snap a picture, think of it a s a pushbroom. It is one long array(the broom) that, as the sattelite travels, collects information. So, like pushing a broom, you collect as it moves.By having a forward facing sensor (26)and rearward facing (-5) you have 2 "brooms" sweeping the sky, collecting the same information, but the large angle creates a paralax(31 I'll leave the math to someone else).

You can do this with 1 sensor by "pointing" in 2 directions, to gain paralax, but that requires moving the platform (sattelite) and doing this repeatadly is a real pain. Essentialy, this sattelite will capture the data in 1 pass, along the same track, in a manner that is easy and predictable for post-processing. I think its a very slick setup, a should provide alot of useful data.

Re:All this...

[Anonymous Coward]

That data of avg. literacy rate of 52% is from 1991 census in India. According to the 2001 census , the avg. literacy rate is 64.8%. [censusindia.net]

Also check out this ...

http://india.eu.org/1963.html [eu.org]

India's literacy rate stands at 64.8%
The Economic Times, Saturday 10 July 2004,

NEW DELHI, JULY 10: As much as 64.8 per cent of India's population is literate while Uttar Pradesh continues to be most populous state followed by Maharashtra, according to details of the 2001 Census released on Saturday.

Re:Not just stereo

[Anonymous Coward]

It's not the first stereo capable satellite: the french satellites SPOT [spotimage.fr] have 3D capabilities (they have two identical cameras).

SPOT 1 was launched in the late 80's.

Re:Imagine the Possibilities

[lliiffee]

Get cool 3D images of Grand Canyon, Yosemite, Everest, Uluru, etc.

Don't get too excited. The process of extracting 3d depth from a pair of 2d pictures is shockingly more difficult than one would initially expect. Given the 2d positions of the same point in both cameras, it is trvial to find the 3d depth, but in practice the problem of finding the corresponding points is extremely difficult. (It is called the 'correspondence problem' and can justifiably be called the holy grail of the field of Computer Vision.) For those who are truly interested, you can actually see how most of the current state of the art stereo algorithms run on a few (easy) stereo pairs here [middlebury.edu].

Re:Not the distance between the cameras

[Emnar]

You forgot to factor in the radius of the earth itself, above which the satellite is orbiting an additional 620km.

The actual forumla is:

((12756km + 620km) * 2 * pi)/360 = 233km per degree

Re:All this...

[peacelife]

No, the taxes are not that high - the highest income tax slab is slightly higher than 30%. The cost of living is much lower in India than in the US, so unless you factor that in, any assumptions/comparisons you make are likely to be wrong. But you have got me thinking about the military expenditures of both the countries. The Bush administration is asking for about $419 billion [armscontrolcenter.org] for its military. That is a truly humungous amount. What do you do with it? That alone is half the global military spending!

And a nitpick which will hopefully bring this post back on topic - the average literacy you mentioned is wrong. It is 64.8% [censusindia.net] according to the 2001 census. The number you gave was for 1991. 14 years can make a lot of difference in a country like India, even given its huge population.

Re:All this...

[danila]

According to the studies that I recall, something on the order of 30% of Americans were functionally illiterate. That basically means they can't understand a written text (except sufficiently dumbed down content, of course) even though technically they are able of reading it.

Re:Not the distance between the cameras

[starfishsystems]

But parallax is measured with respect to a given point. That point is being measured relative to a surface 620 km away, the only difference being its height.

The curvature of the surface is not relevant to the calculation, thus neither is the radius of the earth. To consider the extreme cases, the surface could be absolutely flat (radius infinite), or it could be a point (radius zero). Either way, your two cameras are still 620km away from that surface. The object is still at some other distance which we can measure purely by comparing the difference in parallax between the two.

Also launched a ham satellite: VUSat

[leighklotz]

The same rocket launch also put into place ham satellite [deepikaglobal.com] for use in South Asia. There are other satellites available for personal use (AMSAT [amsat.org] has several, including (Echo 51 [amsat.org]) but VUSat [amsat.org] is focused on use from India and South Asia.

Re:Need clarification

[ghoul]

India doesnt receive much direct aid from the US . Indian poor do receive a large amount of money from US based evangelical groups trying to promote Christianity in India (pretty successfully too Already 2 Indian states have become Christian Majority over the last 50 years )
India keeps losing it best people to the US but now slowly more and more people are staying back and using their brains to run ISRO and DAE (department of Atomic Energy) instead of enriching the shareholders of IBM and Microsoft.
There is great emphasis on tech in India . Engineers are much more respected in society than doctors or lawyers in contrast to the US so a lot of the top brains go to Engineering.

Re:All this...

[Anonymous Coward]

The grandparent post was suggesting that the educated population (e.g. the ones doing space research etc.) would emigrate if they were ignored by the govt. $450m/yr isn't much, but reducing even that in exchange for rice [exaggeration, India actually has a surplus of food, the distribution of which is what requires improvement - ration cards (similar to US welfare) are apparently not properly distributed] would certainly infuriate the elite enough to leave the country. I'm sure the "rust belt" cities here in the US could've had a better fate if they learned how by infuriating those who grow the economy their own prosperity will blacken.

Re:Imagine the Possibilities

[Nilmat]

Yes, but there are advantages to doing this via satellite as well. For example, repeat passes allow observation of subtle changes in topography due to things like subsidence from withdrawal of water or petroleum, glacier movement, tectonic and volcanic activity, etc. Basically, think about all of the applications of SAR (synthetic aperture radar, for non-remote sensers) Interferometry. There are also LIDAR satellites such as IceSAT that observe elevations with great precision along transects. There are actually quite a number of satellites up there with the capability of doing things similar to this, but generally not at this spatial resolution (2.5 m). I'm involved with a group proposing a satellite to NASA that would be used to obverve changes in water heights on floodplains and in rivers, allowing observation of ungauged rivers in remote regions as well as helping to get a handle on discharge from rivers (such as the Amazon) which are impossible to gauge along much of their length.

Re:Never pusued invasion/colonization?

[Anonymous Coward]

East Pakistan is better known as the independant nation of Bangladesh which India helped during its war of independance from Pakistan who used to treat the then East Pakistan as a colony.

Ceylon is better known as the independant nation of Sri Lanka.

Why two cameras needed for stereo

[Thagg]

Many people have posted almost the right answer for why two cameras are needed, one pointing slightly forward, one slightly back, for stereo. That's right, as far as it goes.

But what people are missing is that these are not cameras like you are used to. The pictures they take are not (say) 4k x 4k, they are 4k by 1 pixel. That one-pixel-high image is painted across the surface by the motion of the satellite, generating a very long strip image. Typically, the cameras run continuously.

So, that's why you can't just "snap a photo, move the camera, snap another one". These are not snapshots, they are long strip images taken a scanline at a time. Two fixed cameras are the right answer.

Thad Beier