How does an Earth observing satellite measure the temperature of the atmosphere?

Can they measure temperature at multiple altitudes, or measure the temperature of clouds?

  • $\begingroup$ "Is there a satellite that is open to the public for this?" is a separate question, it's asking for a website, not related to the technology. You can ask for public sources in Earthscience SE or possibly Open Data SE (not sure about that one). $\endgroup$ – uhoh Mar 14 '19 at 6:31
  • $\begingroup$ But "How does an Earth observing satellite measure the temperature of the atmosphere?" is a good question. $\endgroup$ – uhoh Mar 14 '19 at 6:37
  • 2
    $\begingroup$ @Muze, in case you want to find an open dataset for these measurements, the IASI instrument data from MetOp (ESA) is open and can be found here. $\endgroup$ – Alexander Vandenberghe Mar 14 '19 at 9:27

I'm not sure if I understand the basics behind this well enough to explain it but I'll give it a try anyway.

I've looked mainly at this report and on the wiki on satellite temperature measurements.

The basic measurement technique is using an infrared interferometer. The absorption and emission spectra that the instrument measures are dependent on the composition of the atmosphere and the temperature. The composition of the atmosphere at different altitudes is pretty well known.

Measurements at different frequency bands give a solution of the temperature profile using the following formula.

$$T_B = W(0)T(0) + \int_0^{TOA}W(z)T(z)dz$$

$T_B$ is the measured brightness temperature by the satellite. The $W(0)T(0)$ term describes the upwelling radiance from the surface, dependent on the surface temperature, the surface properties, the frequency band that is measured, …

The integral part represents the column of atmosphere underneath the satellite.

$W(z)$ is a weighting function that is specific to the frequency band measured. MSU weighting functions based on the U.S. Standard Atmosphere

By combining measurements at different frequency bands you can get a solution for the temperature profile of the column of atmosphere underneath the satellite. The more frequency bands you measure in, the more resolution (vertically) you will achieve.

I don't know the method that is used to combine these measurements but I assume you can use something like least-squares to get to a solution.

Now for the second part of your question: as explained, they measure the temperature at different altitudes. Clouds mess up the measurements and need to be corrected for, usually using information from other instruments. Cloudtop temperature I believe would be easier to measure, since clouds have a fairly recognizable composition and it should thus not be too hard to extract the temperature using an interferometer.

  • $\begingroup$ wow this looks pretty complicated. I've clicked through Wikipedia to Microwave Sounding Unit and Advanced Microwave Sounding Unit and all the way to... $\endgroup$ – uhoh Mar 14 '19 at 9:43
  • $\begingroup$ these: 1, 2, 3 and it will take a lot of reading to understand how these closely spaced bands can be so specific in their sensitivity to different densities/altitudes. $\endgroup$ – uhoh Mar 14 '19 at 9:44
  • $\begingroup$ @uhoh feel free to add to the answer if you find out more! I agree it's pretty complicated. $\endgroup$ – Alexander Vandenberghe Mar 14 '19 at 16:50
  • $\begingroup$ You're answer is great! I left those there just in case they are helpful to you or someone else. I think it's the basis for a good follow-up question in Earthscience SE. $\endgroup$ – uhoh Mar 14 '19 at 21:36

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