Monday, January 11, 2010

Wow! ...You Can Do That With A Satellite Imagery?

Here is an early candidate for this years confusing reporting on satellite imagery applications award.

From a well known Asian GIS portal:

....BWSSB (Bangalore Water Supply and Sewage Board) has installed bulk flow meters to monitor the flow of water in different areas and to check the wastage of water.

The board is expecting that GIS will help the department in checking the unaccounted for water. BWSSB has undertaken two major pilot projects to study the feasibility of implementing the system. The first of the two is expected to help the department, trace the leakage in the city through satellite imagery.

That's it.....the press release does not explain how.

Which means that lots of people not familiar with how imagery is collected and used will think that a water leak leaves a particular signature that can be recognized in a satellite image and that's how the Bangalore city government is going to keep a tab on leakages.

But that's not how it works. The pipes are buried under asphalt and concrete. For most GIS applications, satellite sensors which image in the visible and near infrared wavelengths are used to collect earth information. These wavelengths cannot penetrate the ground and image the buried water pipes. Even if there are lengths where pipes are exposed there is no way satellite imagery can be used to monitor leakage on a day to day basis.

Why? ...No..its not just that the spatial resolution won't be enough.

M: Where is 007 right now Q?

Q: ...(peering on towards a large screen)...Hmm...looks like he is skiing in Austria...his thermal trace is clearly visible..

Despite this fantasy land depiction of satellite imagery, there is no real-time  feed of data in the real world of remote sensing and imagery analysis. Remote Sensing satellites, like the ones used by Google Maps and ISRO's Bhuvan,  spin around the earth and image the same location every few weeks or so. They simply can't be used to monitor just one location for apps like water leakage.

Besides a lack of understanding of spatial and spectral resolution  I think this is the biggest misunderstanding about satellite imagery that persists in popular imagination. Which is why the media keeps reporting that high resolution imagery can now be used to count the number of lions in Gir forest and to locate fish shoals.

So... can imagery to be used in applications like monitoring leakage from water pipes?

Yes, but their role will be as a reference to location. A city GIS will have several thematic layers...say roads, building footprints, green zones, cables and pipes all overlain on a geographic reference layer which could be a topographic map or a high resolution satellite image. The image being used as a backdrop may be six months or even a year old. The actual information about leakage is obtained from instruments like flow meters. The location of each flow meter along the pipes is known. This information by cross referencing the pipe layer with the imagery will help repair crews familiarize themselves with the exact location of the leaking pipe.

Tip: Rashid's Blog


  1. E.C Rifareal- if you visit again, don't try to advertise via my blog.

  2. It is nice to read your blog posts about GIS. Quite informative too. Thanks for sharing.

  3. navya- if you work in GIS it would be great if you can write more on GIS Industry in India on your blog.

    Rashid- thanks for visiting.

  4. What about radar instruments on satellites?
    They penetrate the ground for soil moisture measurements at least and I have understood that underground pipes can be distinguished as well.

  5. remote sensing satellite sensor including radar cannot do real time monitoring.. yes moisture patches can be picked up but they can by visible and infrared as well.. and those underground pipes..the city already knows where they are..