Saturday, February 4, 2017

Satellite Temperature Estimates

Back in December I mentioned that I had found a way to begin working with land surface temperature estimates from the Suomi NPP satellite (launched in 2011); the modern radiometer on the satellite measures infrared radiation at a spatial resolution of 750m, which allows for nice high-resolution estimates of surface temperatures when clouds are absent.  I've recently also decoded similar data from the MODIS instrument on the TERRA and AQUA satellites, launched in 1999 and 2002 respectively.  The MODIS resolution is about 1km.

Here are a couple of images showing estimates of the minimum surface temperature observed by these satellites on January 18 over the Fairbanks area and points eastward into the hills; this is the day that temperatures bottomed out during the cold snap.  I've interpolated the data to a 750m grid in both cases for consistency (click to enlarge the images).  The similarities are striking, but greater spatial detail is evident in the S-NPP (lower) image, as expected.

It's gratifying to see that both maps show the cold conditions on the Salcha River in the bottom right; the Salcha River RAWS (SLRA2) reported -59°F, and the satellite data support this very cold reading.  On the other hand, the -65°F reported by the Upper Chena River HADS site (UCHA2) is not supported and was almost certainly in error.

Below is a comparison of the minimum temperatures (in °F) reported at each of the sites marked on the maps.  The agreement is, in my view, quite impressive, with only the Stuart Creek RAWS seeing a substantial difference if we exclude the Upper Chena HADS site.  At both Stuart Creek and at the Salcha RAWS, the estimates are better for the S-NPP, which probably reflects the superior resolution of the S-NPP instrument.



  1. Tried to post a comment yesterday but it apparently disappeared. Anyway, was surprised to see the -65 reading at UCHA2 (Chena R nr Two Rivers gage), so downloaded the data for Jan 17-19 from the USGS site ( the lowest reading for those days is -53.8, so the -65 on the HADS site maybe from posting uncorrected data? The coldest we had at our place near 10 mile CHSR was -41.5, which was the coldest in about ten years. So much for global warming! Enjoy your blog. Jon

  2. Jon, thanks for looking into this. A bit more digging reveals it is a Celsius-Fahrenheit conversion problem... -53.8°C=-64.8°F. USGS shows the temperatures in °F but every other source shows the data after erroneously performing the conversion. See for example the bogus values on

    This is not happening for all HADS sites so I'm not sure what the issue is here. Hopefully it can be fixed soon.

    Do you have long-term weather records from your place?

  3. We have weather data for about ten years. It's an old Hobo station from one of my wife's projects that was trashed by a moose or bear. She repaired it and set it up for testing, but they never needed it again. Now that she's retired, she keeps it going and sends the data to her old boss. Not sure if he does anything with it. It's downloaded into excel, probably a pretty big spreadsheet by now. You're welcome to it if it'd do you some good. Might be interesting to compare to the Little Chena or airport weather data.

  4. With the forecast cold snap this weekend it might be a good time to further calibrate the satellite's temp estimates.

    Might be the last chance for a few months as insolation is affecting daily temperatures. Saw the first frost melt on my dark roof edge and gutters earlier this week.


    1. Yes, it will be interesting to see what the satellite reveals in the upcoming cold. I'm working on a Google Maps interface to view the near-realtime satellite temperature estimates...

    2. Won't take long to make ice cubes in Howard Pass/Brooks Range the next few days.