Retrieving orbital track, scan and time information

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jonathanschultz
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Joined: Tue Jun 09, 2020 9:45 pm America/New_York

Retrieving orbital track, scan and time information

by jonathanschultz » Tue Jun 09, 2020 10:36 pm America/New_York

I'm working on a research project that aims to reproduce a number of historic wildfires based on data, including notably satellite data (MODIS and VIIRS) from FIRMS. To do this I am trying to solve two related problems:

1. How to translate the track and scan fields in the FIRMS data into an area on the ground that is covered by that data point. I guess that means knowing the angle at which the satellite is tracking, but ideally I'd just like a formula that I can feed to my GIS software.

2. How to detect when a hot spot has cooled, that is when the satellite makes a pass without detecting a hot spot. The FIRMS fire map indicates that orbital track information is available from https://www.space-track.org but other than some amusingly retro-modernist fonts I can't seem to find anything useful there.

Many thanks in advance for your assistance.

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ASDC - rkey
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Re: Retrieving orbital track, scan and time information

by ASDC - rkey » Wed Jun 10, 2020 4:48 pm America/New_York

Thank you for your question. A Subject Matter Expert has been notified and will answer your question shortly. Please stand by!

In the meantime here is a great reference:
https://earthdata.nasa.gov/faq/firms-faq

masuoka5515
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Joined: Mon Jun 15, 2020 12:20 pm America/New_York

Re: Retrieving orbital track, scan and time information

by masuoka5515 » Mon Jun 15, 2020 12:52 pm America/New_York

With respect to the questions below:

1. How to translate the track and scan fields in the FIRMS data into an area on the ground that is covered by that data point. I guess that means knowing the angle at which the satellite is tracking, but ideally I'd just like a formula that I can feed to my GIS software.

For each detected fire the latitude/longitude is provided for the center point of the spatial element. The track is the north south dimension in km of the spatial element and the scan is the east west dimension. This is described in the FIRMS FAQ https://earthdata.nasa.gov/faq/firms-faq for MODIS. So area covered would be a rectangle centered on the lat/long with dimensions as specified above.

2. How to detect when a hot spot has cooled, that is when the satellite makes a pass without detecting a hot spot. The FIRMS fire map indicates that orbital track information is available from https://www.space-track.org but other than some amusingly retro-modernist fonts I can't seem to find anything useful there.

In FIRMS the orbit tracks are shown with the center point of the scene appearing as a filled in circle along the orbit track. These appear for each instrument/spacecraft, e.g. MODIS Terra, MODIS Aqua, VIIRS on Suomi NPP and so on. But I that should be irrelevant to your question which was when does a satellite makes a pass without detecting a hot spot in the area of interest. If you have downloaded the historical data for specific areas from FIRMS by instrument and have imported these data into a GIS and have made a correction for the growth in the spatial elements away from nadir due to the scan geometry (your question 1). Then you should be able to answer the question, when was the last time MODIS or VIIRS detected a fire at that location. I recommend reviewing the caveats to using MODIS and VIIRS for fire detection under the FAQs because factors like cloud cover come into play.

I can reach out to experts on the active fire product, geolocation or FIRMS if you have additional questions .

My email address is:
Edward.J.Masuoka@nasa.gov

jonathanschultz
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Re: Retrieving orbital track, scan and time information

by jonathanschultz » Mon Jun 15, 2020 10:11 pm America/New_York

Thank you for your response. I'm afraid I'm still having trouble following.

> So area covered would be a rectangle centered on the lat/long with dimensions as specified above.For each detected fire the latitude/longitude is provided for the center point of the spatial element. The track is the north south dimension in km of the spatial element and the scan is the east west dimension. This is described in the FIRMS FAQ https://earthdata.nasa.gov/faq/firms-faq for MODIS. So area covered would be a rectangle centered on the lat/long with dimensions as specified above.

I've tried specifying the rectangles as you describe and it is immediately clear that something isn't quite right. That is, rather than adjoining end-to-end, each rectangle is offset with respect to its neighbors. My understanding of this is that the satellite isn't moving in a straight North-South direction, but at an angle (this is also clear from the FIRMS fire map https://firms.modaps.eosdis.nasa.gov/map - click on 'Orbit Tracks and Overpass Times' then select one or more satellites and you'll see what I mean), and the rectangles need to be rotated to reflect that angle. My problem is I can't work out what the angle is, and that is what I am hoping to learn.

> Then you should be able to answer the question, when was the last time MODIS or VIIRS detected a fire at that location.

The downloaded data only specifies when a hotspot was detected and not when a pass was made without any hotspot detected. So I am no closer to having an answer to my question of how to know when the hotspot has cooled. I believe the only way to answer the question is by testing for the hotspot at the time of the next satellite pass, which is why I want to learn how to retrieve or calculate that time.

> I can reach out to experts on the active fire product, geolocation or FIRMS if you have additional questions .
> My email address is:

If you could reach out to the relevant experts I would be most grateful. I've continued the discussion on the forum so that others might benefit but if you prefer I can also email you directly.

masuoka5515
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Joined: Mon Jun 15, 2020 12:20 pm America/New_York

Re: Retrieving orbital track, scan and time information

by masuoka5515 » Wed Jun 17, 2020 5:44 pm America/New_York

Jonathan:

Since I don't have your email and you have mine, kindly contact me via email. I am happy to answer your questions but I am puzzled by a couple of them and I would like to following up with you about them.

Ed Masuoka

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