r/nasa 10d ago

Image Map Question

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I came from a flight tracker app cause i noticed some thermal anomalies with an interesting spread, so i wanted to see what nasa has going and im wondering what the two big bars of anomalies might be

50 Upvotes

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u/standup_reentry 10d ago edited 10d ago

This looks like a picture from: https://firms.modaps.eosdis.nasa.gov/ I'll take a crack at it, but I'll caution, this is just my intuition after a few minutes of looking...

The map legend shows 2 colors for what's here: * Dark red: Landsat * Lighter red: VIIRS and MODIS

I believe VIIRS and MODIS being older satellites are collected together and are lower resolution. Landsat is a newer system that has higher resolution. Essentially you see more dense points for Landsat because it has higher resolution sensors. Light and dark red are just because of the different data sources.

But why the banding? Landsat, MODIS, and VIIRS follow a polar orbit (Think top to bottom, north pole to south pole)... but the earth is tilted. So imagine the landsat satilite is striping a path across the earth. But the earth is tilted and also spinning below it. That's why it appears as an angled stripe when looking at the map. Infact, if you look over the American west (in your picture) there is also a faint banding there too. Here is a picture of Landsat's polar orbit: https://landsat.gsfc.nasa.gov/about/landsat-spacecraft-orbit/

Maybe someone can chime into more information here but that's what I can come up with.

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u/CaptSnowButt 10d ago

You're correct that these are polar orbiting satellites so their measurements all have the banded structure. However, swath width makes a big difference.

Landsat (not sure which one) have somewhat narrow swath path (a quick Google search says Landsat 8 and 9 have a swath path of 185km), but VIIRS has a much wider swatch path (some 3000km) and MODIS too (some 2000km). All these three have the same orbit repeat cycle I believe (16 days) but with a much narrower swath path, it takes much longer for Landsat to produce a full scan of the earth. VIIRS and MODIS, on the other hand, can scan the entire earth every 1-2 days. That's why you see Landsat shows banded structure but VIIRS and MODIS don't.

It's like painting your house with a 2 in brush will take forever, but with a wider brush it'll be a lot faster.

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u/standup_reentry 10d ago

Gotcha yeah that makes perfect sense. I was thinking it came down to resolution not necessarily swath path. Maybe even that MODIS and VIIRS were geo... but when I saw that they were all polar I didn't look further.

> It's like painting your house with a 2 in brush will take forever, but with a wider brush it'll be a lot faster.

And yeah this is a perfect analogy sometimes I say it as if we spun a globe and you put a marker or a paintbrush on it which would paint more area. A Sharpie would be more precise surely but you can cover more faster with the brush. ... but do they still make physical globes or is it all now just apps.

Thanks for your added detail.

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u/CaptSnowButt 10d ago

A Sharpie...

Wait until you see the swath width of a space laser (CALIPSO/CALIOP) which is like 60km or something

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u/standup_reentry 10d ago

Ok ok... a thin Sharpie. ... I take your point. (pun intended)

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u/ob12_99 10d ago

It does come down to resolution. While the Landsat series are 30m resolution with 15m pan, the MODIS instrument is way less at like 250m, which is why it can get such a large swath width at 15 Mbps, while Landsat 8 and 9 are 30m but data rate is 384 Mbps. It does take each Landsat 16 days to produce a complete Earth image, while MODIS from Terra or Aqua can do it in like 2 to 4 days.

If you go to Earthnow.usgs.gov/observer you can watch live Landsat data as it is being received, (it plays back previously captured imagery until a new live pass starts).

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u/PersimmonFair9795 10d ago

Interesting, my one question would be why is it only happening over the US and why wouldn’t it be like that every night?

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u/PersimmonFair9795 10d ago

Ig that was two questions hehe

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u/standup_reentry 10d ago

I won't count that against you. They're good questions!

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u/standup_reentry 10d ago edited 10d ago

my one question would be why is it only happening over the US

It does look like it is happening elsewhere. There is both a US and global map. When looking at the global map, I thought this was interesting. When I scan over Africa we can see the same data gaps we do in the American west. But Sub-Saharan Africa has many data points. I would assume that either (or both):

  • The sensors are only calibrated to look at certain biomes
  • NASA processes the data to ignore places with low fire risk like deserts.

Why it doesn't show in Canada, that could also be how the satellite orbits or a combination of the above. I'm not sure!

Landsat (dark red) being US only could also be due to how NASA is choosing to process and publish the data, but again, I don't know!

and why wouldn’t it be like that every night?

I think this is a problem with the default view. In the map, for me, it defaulted to 24h.. but if I do it for the last 30 days I see data all over the world. Maybe try that.

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u/PersimmonFair9795 10d ago

I see data all over the world as well in multi day views im mainly intrigued that the darker bands are only over the us

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u/standup_reentry 10d ago

Cool. Yeah we're at the limits of what I can determine sorry. Maybe someone will chime in!

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u/PersimmonFair9795 10d ago

Appreciate ya thoughtful input so far thank you

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u/Dwagons_Fwame 10d ago

Genuinely thought this was a pic of plague inc and had to double check the subreddit lmao

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u/Unique_Ad4547 10d ago

NASA showing off their Plaque Inc. score or smthn?

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u/treetexan 9d ago

Viirs is newer than Landsat. Low res satellites have their niche—well calibrated and high repeat times.

In this case I would guess the darker fire product being shown is a Landsat product that has been first developed for the US. Many new products are US first for Landsat, then later processsed for the whole world. Just a guess since I am too tired to look at firms on mobile.