Your fire mapping explanations are woefully lacking

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John Radford

12 Sep, 2020 03:11 PM

I am trying like hell to understand exactly what I am seeing on fire maps, specifically trying to understand the abbreviations for VIIRS data and, of course, what the spot really mean.

- MDT is what? I cannot find anywhere except maybe it means Mountain Daylight Time, which is of course absurd for a satellite.
- so WHEN was a VIIRS image taken? What do the timestamps mean?
- the Suomi NPP satellite zips by at 16,000 mph so how many images does it take of a fire such as the Creek Fire? ONE?
- Creek Fire spot timestamps, for instance, vary WAY too much. How is it possible for times, such as I see right now (9/12 08:00 PDT for me) to be "9/11 03:48 MDT" and another be "9/11 04:36" for instance? How many VIIRS devices are there if times vary like that? It is literally impossible for a satellite flying that fast to take a photo almost an HOUR after an earlier one in the same overflight !!!! Utterly impossible.
- if on a subsequent pass a hotspot from a previous time is not shown as current, does that mean the old hotspot cooled below some threshold or the fire is even "out"?
- I see innumerable examples where hotspots for the <12 hr data set appear WITHIN a zone of many <24hr hotspots (different color) but the new <12hr hotspots do not show up anymore where the old hotspots were. In other words, does that mean the older hotspots are no longer hot? Really?

  1. 1 Posted by John Radford on 12 Sep, 2020 03:37 PM

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    I know the timestamps could be 101 minutes apart since the orbital period is 101.4 minutes. But there are timestamps 54 minutes apart, 48 minutes apart, etc.

  2. Support Staff 2 Posted by Ben Lantow on 12 Sep, 2020 04:57 PM

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    Hi there,
    A discussion of sources and methods is found at: http://caltopo.com/about/2020/08/20/summer-wildfires/

    Times are converted from UTC to MDT for ease of use.

    The other point of confusion seems to be the fact there are two different VIIRS satellites both feeding data onto the fire activity layer, it sounds like you're seeing hot spots detected by both which are on different orbits.

    Hot spot detection is one way to track fire growth and changes. Hot spots are mapped as they are detected. If the same hot spot is present for multiple passes that location will be updated, if a hot spot hasn't been detected on the most recent pass, or on several recent passes you can infer that the temperature there has decreased, however you cannot determine if a fire is "out" or contained from hot spots alone which is why NIFC fire boundaries are also displayed on the map, see the above link for more discussion about sources.

    Best,
    Ben

  3. Ben Lantow closed this discussion on 12 Sep, 2020 04:57 PM.

  4. John Radford re-opened this discussion on 12 Sep, 2020 07:22 PM

  5. 3 Posted by John Radford on 12 Sep, 2020 07:22 PM

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    I had gone to the "summer-wildfires" page over and over and it did not answer my questions. I don't think you, for whom this may all seem obvious, quite get my questions. Please bear with me, OK? By the way, I am a huge fan of Caltopo and mention it to anybody and everybody. I subscribed long since and use it constantly in planning trips, making maps to print or take on my phone, and for all manner of other activities requiring geography-related info. KUDOS!

    In fact, I am right now in a mandatory evacuation zone of the Creek Fire. I have been posting multiple observations and updates every day this week to some 4500 NextDoor users in my area and have gotten amazing thanks and support for that, much of it actually thanks to YOUR website mapping of the fire info.

    But I have struggled finding anywhere explanations for my lingering questions. So, questions and suggestions:

    - please state somewhere MDT really DOES mean Mountain Daylight Time. It is NOT at all obvious and makes absolutely no sense automatically. One assumes the VIIRS program affixes the timestamp and why on Earth (or out of Earth) would they ever use MDT? I'm fine using Mountain time but it should be explicit. I assume the conversion is made by Caltopo, not NASA or NOAA.

    - please state explicitly there are TWO VIIRS satellites.

    - are you sure about that? I looked for JSP-1 (typo in your site - should be JPSS) and found nothing. Instead I found JPSS-1 and JPSS-2 which are not even in service yet! What gives? Is NOAA's web site out of date (likely) and these satellites ARE currently in use?

    - again, what is happening with hotspot imagery? If a satellite makes a pass, does the VIIRS system record and broadcast ONLY those spots, in an entire area, that are still hotspots at that time? So when <12hr old observations are made that means "Hey, folks, no RED dot, ain't hot"? I already get it that other colors are for important historical interest. But I was just not sure that a lack of RED dots meant literally everyhere they were absent meant NO hotpspots were found in those areas anymore (cooled).

    - please state somewhere that the map timestamps are for "time of observation" and not some post-observation processing or downloading time. I was confused because the times made no sense.

    - how exactly is a hotspot identified and/or what does a hotspot indicate, precisely? What is the temperature criterion or what are the criteria anyway? I assume, and it seems obvious, hotspots grade down to warm spots and someday become cold. So where is the cutoff?

     THANKS!

  6. 4 Posted by John Radford on 12 Sep, 2020 07:59 PM

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    Also, JPSS-1 and JPSS-2 satellites are NOT listed in my satellite tracker app. So who IS posting the extra VIIRS sightings?

    ______________________John Radford32264 Road 224 North Fork, CA 93643
    650-847-5085650-823-5461 cell

        On Saturday, September 12, 2020, 9:58:00 AM PDT, Ben Lantow <[email blocked]> wrote:

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  7. 5 Posted by John Radford on 13 Sep, 2020 02:15 AM

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    Ben,
    Thanks for the reply earlier.

    Over the past couple of days, I had already gone to the "summer-wildfires" page you suggested today, over and over and it did not answer all my questions. I don't think you, for whom this may all seem obvious, quite get my questions. Please bear with me, OK? By the way, I am a huge fan of Caltopo and mention it to anybody and everybody. I subscribed long since and use it constantly in planning trips, making maps to print or take on my phone, and for all manner of other activities requiring geography-related info. KUDOS!
    In fact, I am right now a stay-behind in a mandatory evacuation zone of the Creek Fire. I have been posting multiple observations and updates every day this week to some 4500 NextDoor users in my area and have gotten amazing thanks and support for that, much of it actually thanks to YOUR website mapping of the fire info which I have tried to understand and pass along. I have repeatedly posted your website as a great fire watch source. It is amazing how many folks, especially evacuees, are desperate for current info.
    In that process, I have struggled finding anywhere explanations for my lingering questions. So, some questions and suggestions, not in order of importance:

    1 - please state somewhere MDT really DOES mean Mountain Daylight Time. It is NOT at all obvious and makes absolutely no sense at first. One assumes the VIIRS program affixes the timestamp and why on Earth (or out of Earth) would they ever use MDT? I'm fine using Mountain time but it should be explicit. I assume the conversion is made by Caltopo, not NASA or NOAA.

    2 - please state explicitly there are TWO VIIRS satellites:  "Suomi NPP" and the new "NOAA 20" (which you accidentally named JSP-1 instead of JPSS-1, which was later changed anyway to NOAA 20).
    3 - please state somewhere that the map timestamps are for "time of observation" and not some post-observation processing or downloading time. I was confused because the times made no sense at one point. I'm still not 100% certain that's the case though it really only makes sense.

    4 - can I assume with certainty that each pass of the satellite (roughly twice a day each) starts with a blank canvas, so to speak, and so the new detections in a 12hr period are all of the hotspots there are? That is "If there's no RED dot it ain't hot." The other colors are historical data only and will register as hot only if they are re-recorded as such?  I was just not sure that a lack of RED dots meant literally everywhere they were absent meant NO hotspots were found in those areas anymore (cooled enough). Obviously, a landscape takes some time (maybe weeks) to fully cool. But a lack of a red dot should mean there's no hotspot in a given location, period.

    5 - how exactly is a hotspot defined already? I simply cannot find a definition that means anything. What is the temperature criterion or what are the criteria anyway? Obviously, hotspots grade down to warm spots and someday become cold. So where is the cutoff? Thus an entire landscape could be smoldering but the VIIRS tools would show a total blank space unless there was ... what? ... a specific intensity or specific wavelength light or critical level of energy (megawattage) or what? I have spent hours today trying to find ANYBODY who states what the definition of a "hotspot" is. 
    6 - please share that definition of "hotspot" in your Caltopo explanations. It should be damn simple, right? Why has nobody, from NASA to the rest of the world not provided a definition? I KNOW there is a precise definition because the algorithms require one. I also assume "well, it's more complicated than that."
     
    THANKS!

    John

    ______________________John Radford32264 Road 224 North Fork, CA 93643
    650-847-5085650-823-5461 cell
     

        On Saturday, September 12, 2020, 9:58:00 AM PDT, Ben Lantow <[email blocked]> wrote:
     
       
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  8. Support Staff 6 Posted by matt on 13 Sep, 2020 04:34 PM

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    John -

    I understand your frustration. Since the original lightning-generated fires three weeks ago, we've been scrambling just to keep up. Personally, I've had two 3 hour mornings off in the past 3 weeks, and the rest has been spent on work, almost all fire related. Our primary focus was on rolling out GOES imagery and fire detections to fill in the gaps between VIIRS/MODIS passes, since frustration of the slower update frequency of those satellites was the primary complaint we've heard from users. We've also had to invest considerable time in scaling the site up to meet increased demand, and at the same time we're also trying to make changes to the site and the app that are invisible to most recreational users but critical to first responders involved with the fire. An example of this is the ability to set whether a folder is visible on page load, which may seem minor, but can make a world of difference when you have hundreds or thousands of points loaded onto a map. In short, there's only so much we can do.

    1. The satellite timestamps are in UTC, and we convert those for our US-centric audience. We can't display different tiles to different people based on where they live, so we picked one time zone, and MDT seemed to split the difference pretty well. Long term, I'd like to tag detections with the timezone they're in and show local times for all detections, but that's not something we can do immediately.

    2. We are behind on this because the second satellite only started reporting detections this year, and we only integrated it after the original lightning fires. So the map layer still shows aqua vs terra, but only "viirs".

    3/4/5/6 - All I can tell you is that we take the data from the government and do our best to present it as-is. Timestamps should be the time of observation. The lack of a red dot means no detection reported from the past 12 hours, but sometimes due to the timing of the satellite processes and the processing latency, you'll see a place turn orange, only to turn back to red in an hour or two when new data comes in. And it only means the area wasn't hot enough to register as a detection, you can definitely still have lingering fires within a burn zone (not just embers on the ground) and not have have them be intense enough to show up as satellite detections. But if I get what you're asking with 4, yes, the satellite reports everything that appears hot, it doesn't filter out pixels that were detected previously.

    I don't know the specific qualifications for a hotspot. We get the data as hotspot detections not raw satellite bands, and people more qualified than I have figured out how to map between the two. All we can do is reporting the data as it's presented. I know that's not a satisfying answer, and that there's frustratingly little precision in all of this, but that's the best I can tell you.

    • Matt
  9. 7 Posted by John Radford on 13 Sep, 2020 04:45 PM

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    Matt,
    Thanks for all that. Some day somehow I'd still like to find out what the "hotspot" criteria are. Why so hard to find?? Oh well.
    I appreciate all you guys do at Caltopo. I used to buy USGS maps since 1974 (lived 25 minutes from Menlo Park) and I've been using all the web-based mapping sites since 2005 and bought several (waste of money like full set of CDs for CA maps ... hard to use and hardly used).

    Caltopo is a wonderful, the BEST, mapping service ever! There's still good reason to buy the odd (usually large) printed maps but a whole lot less reason to buy smaller maps than ever before.

    Yet again, I put your link in my Creek Fire update this morning.
    John

    ..........................................
    Snippet from 9/13 Creek Fire update for NextDoor groups I belong to:

    ______________________John Radford32264 Road 224 North Fork, CA 93643
    650-847-5085650-823-5461 cell
     

        On Sunday, September 13, 2020, 9:34:41 AM PDT, matt <[email blocked]> wrote:
     
       
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  10. 8 Posted by fogmachine on 13 Sep, 2020 04:57 PM

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    The criteria are spelled out in NASA's VIIRS Users Guide.
    It's not easy reading and assumes some background, but it's all there.

    Remember that CalTopo doesn't use raw data, it uses a processed product like those described in Section 3. There are many data VIIRS sets available, perhaps it uses this Near Real Time product.

  11. 9 Posted by John Radford on 13 Sep, 2020 05:24 PM

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    Thanks! I have my homework for today.

    Sent from Yahoo Mail on Android

      On Sat, Sep 12, 2020 at 12:58 PM, John Radford<[email blocked]> wrote: Also, JPSS-1 and JPSS-2 satellites are NOT listed in my satellite tracker app. So who IS posting the extra VIIRS sightings?

    ______________________John Radford32264 Road 224 North Fork, CA 93643
    650-847-5085650-823-5461 cell

        On Saturday, September 12, 2020, 9:58:00 AM PDT, Ben Lantow <[email blocked]> wrote:

    |

  12. 10 Posted by John Radford on 13 Sep, 2020 06:18 PM

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    Actually I saw that file yesterday but could not find the English translation and my eyes glazed over. I am now trying to translate. Not going well.

    ______________________John Radford32264 Road 224 North Fork, CA 93643
    650-847-5085650-823-5461 cell
     

        On Sunday, September 13, 2020, 9:57:11 AM PDT, fogmachine <[email blocked]> wrote:
     
       
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  13. 11 Posted by fogmachine on 13 Sep, 2020 06:26 PM

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    Yes, converting dirty data from low-power satellites 520 miles above the ground into usable fire data in 1000x1000ft squares is PhD-level science. Good thing we have PhD-level scientists interested in really hard problems.

  14. 12 Posted by John Radford on 13 Sep, 2020 06:36 PM

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    Yes! Like if someone told me "make us a space satellite; we'll give you a million years to do it". Never get done. There's a good book germane to the subject of how ALL our modern tech has depended on people who had an almost ferocious attention to detail:
    https://www.goodreads.com/book/show/35068671-the-perfectionists
    Great and eye-opening read.

    ______________________John Radford32264 Road 224 North Fork, CA 93643
    650-847-5085650-823-5461 cell
     

        On Sunday, September 13, 2020, 11:26:05 AM PDT, fogmachine <[email blocked]> wrote:
     
       
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  15. Julie closed this discussion on 14 Sep, 2020 05:30 PM.

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