Elusive Earthquake Imagery

April 29th, 2015 by Adam Voiland
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Clouds obscuring the Operational Land Imager’s view of Kathmandu, Nepal.

Several readers have asked us to post satellite imagery related to the earthquake that struck Nepal on April 25, 2015. While we regularly post imagery of natural hazards, the weather and the satellites haven’t cooperated in this case.

Some people assume NASA’s satellite fleet can collect images of virtually any part of the world in near-real time, but the reality is more complicated. The orbital track of the satellites and the specific capabilities of the sensors on board determine whether we have imagery to share. In the case of Nepal, things haven’t lined up in our favor.

NASA did acquire imagery of Nepal soon after the earthquake. The Aqua and Terra satellites capture images of Nepal every day with their identical Moderate Resolution Imaging Spectroradiometer (MODIS) sensors. Note, however, the words “moderate resolution” in the name. Each MODIS pixel corresponds to 250 meters of the Earth — not 1 meter or less like you will find if you zoom all the way in on Google maps. MODIS does a fantastic job of showing a broad area, but if you compare an April 22 MODIS view of Nepal with an April 27 view, you’ll see the sensor doesn’t have enough spatial resolution to see changes caused by the earthquake. What’s more, it has been rather cloudy since the earthquake anyway.

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Mount Everest before and after the earthquake. Not much change is visible because of a fresh coat of snow and cloud cover. The April 23 image was acquired by the Operational Land Imager on Landsat 8. The April 28 image was acquired by the Advanced Land Imager on Earth Observing-1.

Other sensors like the Advanced Land Imager (ALI) on Earth Observing-1, the Operational Land Imager (OLI) on Landsat 8, and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on Terra have much higher spatial resolution (10, 15, and 15 meters per pixel respectively…good enough to see individual buildings). But each satellite passes over Nepal much less frequently. OLI, for instance, captured imagery of Nepal on April 23, but it isn’t due for another pass until May 9. ALI did get an image of Mount Everest on April 28, but as shown in the images above, there’s no noticeable sign of the earthquake and avalanche due to a fresh coating of snow and some cloud cover. ASTER also was clouded out.

It’s also possible for the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite to detect the widespread blackouts that have occurred since the earthquake but, again, the weather has not cooperated. As you can see in the images (below) tweeted by NASA researcher Miquel Roman, clouds blocked the satellite’s view on April 25 (below), 26, and 27.

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Why doesn’t NASA have sensors with extremely high spatial resolution (less than one meter per pixel) that like some commercial satellite companies do? (Some of those satellites have glimpsed damage to individual structures and shown groups of people congregating in streets.) That’s a complicated subject that would need a much longer blog post to explore properly, but the short answer is that NASA’s emphasis is on the broad view—using medium- and low-resolution imagers to understand macro scale processes on Earth.

NASA sensors are sometimes useful for disaster response and often provide a unique and memorable view of an event like a landslide or wildfire. Yet the strength of satellites like Terra, Aqua, Aura, Landsat, CALIPSO, Cloudsat, GPM, OCO-2, Aquarius, and GRACE is that they drive cutting-edge science by providing global perspective. Want a global map  of the world’s fires? Or global view of sea surface temperatures? A map of ground water? A record of how Arctic ice has changed over decades? A view through a smoke plume as it drifts from Asia to North America? A three-dimensional perspective on the world’s forests?  That’s where the NASA satellite fleet shines. For high-resolution imagery of specific events…well, there are plenty of other organizations that specialize in that.

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13 Responses to “Elusive Earthquake Imagery”

  1. Ellen says:

    Quite a few news media outlets have posted what they call “satellite images of Nepal before and after” (Google it). Are those really satellite images, or are they airplane images mislabeled as satellite images? (In fact, I have the same question about Google Maps when zoomed in close enough to see cars.)

    • Adam Voiland says:

      Ellen, yes, there are before and after images from satellites circulating in the news. There are several commercial satellites that collect very high res images in orbit, and I’ve seen images from them showing up in the news. For instance, Time ran before and after satellite images from Digital Globe. The company has a blog post about their response to the earthquake you might find interesting. There are other mechanisms for getting high-res commercial imagery out into the media as well. As one example, take a look at the International Charter. They have released imagery from Pleiades.

      • Ellen says:

        Thanks very much for the prompt answer and links. That clears up a confusion I’ve had for some time.

        And thank you for keeping us up to date on planet Earth from NASA’s eyes in the sky.

  2. suma says:

    Ok..so NASA did not have capability collect anll images,, why dont nasa put its strength to observe earth first,,
    Before proceeding to other planet!!
    I really can not belive you have reached to Mars!
    But you did not even have the technology to predict the natural disasters!!
    And your digging the MARS to find out lives!!
    But you did nt even have the capasity to find where the vanished MH370 flight!!
    Please do things only which are useful to lives on earth at present, you no need to think about other planet Lives!!

    • Adam Voiland says:

      Suma, that’s a political question better suited for members of Congress. The Earth Observatory’s mission is to report on the imagery and data from NASA satellites that *are* in orbit.

  3. Niels C. Nielsen says:

    Nice illustration with Earth, Moon and all the NASA satellites. Is that avaiable as a poster? Or perhaps downloadable in high resolution?

    Best regards from Denmark

  4. Jonathan says:

    Assuming that this description of NASA is accurate, it would seem that as a government agency,
    There would be enough value in at least ensuring the optical capability
    of NASA’s equipment for viewing and studying Earth if not for Educational purposes then
    at least for “National Security” purposes , which allegedly is of utmost concern to the US Government
    when being held accountable for citizen’s tax money.

    “The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research.”

    So, while it isnt necessarily the US Governments responsibility or business to
    keep track of the safety of other nations, it is irresponsible to try to
    study other planets with the hope of colonization when you dont
    even have a total understanding of your own planet nor can you fully
    acquire the visual data to do so because there is apparently no money or rather priority or even value
    available to improve your lacking equipment.

    Google Earth satellites are extremely detailed and frequently updated. The resolution of which
    Is likely lowered to deliberately mask too much detail. Surely this visual data of Earth is also available
    In realtime, at least to Google. But admitting this capability would cause regular citizens
    to question how a natural disaster could be easily spotted or foreseen yet
    no one is warned to evacuate. Perhaps by denying their own capabilities, the
    Government dodges criticism and responsibility and even financial begligence
    with spending.

  5. Adam Voiland says:

    Jonathan, other parts of the federal government do focus on higher-res imagery. You may find this release from the National Geospatial-Intelligence Agency informative.
    https://www.nga.mil/MediaRoom/LeadingStories/Pages/NGAopenspublicwebsite.aspx

    Google Maps is not updated as much as you might think. https://support.google.com/earth/answer/187961?hl=en http://www.gearthblog.com/blog/archives/2010/10/how_often_does_google_update_the_im.html
    http://blog.zagg.com/how-often-does-google-maps-get-updated/

  6. Attila says:

    Is there any other satellite product from NASA which would show the difference of the surface due to that earthquake in Nepal? For example radar interferogram? This could be with explanation well exploring the topic, I know earthobservatory is strong in that.