Eli being a glutton for punishments and carrot was easily led astray by the likes of Barry Bickmore describing a usual Moncktonian perambulation (aka a trip around the mulberry bush). Seeking amusement Eli was going thru the comments at Willard Tony when this appeared in the LCD from Roy Spencer
"The quoted statement is incorrect as it stands. PRTs are used to measure the temperature of the onboard (warm-point) calibration targets. The cosmic background (cold point) is assumed to be 2.7 K (or something close to that..it doesn’t really matter). PRTs are laboratory standard and highly stable, each one being carefully calibrated before launch.
Those two calibration points are used to calibrate the Earth-viewing data.and the AMSR-E calibration is a special case of poor design…the warm target was made of a material with low thermal conductivity. The instrument was designed in Japan by engineers just coming up to speed on the technology, and it should never have been approved by NASA in the first place. But, the instrument was “free” to NASA, so there was less scrutiny. I say all this as the AMSR-E U.S. Science Team leader."Dr. Roy was explaining to the assembled WattKnots how the (A)MSU system works by interpolating the signal between deep space (2.8K) and a hot target. The hot target has a number of platinum resistance thermometers buried in it and a pseudo black body surface (black is the most difficult color). The targets are technically complex. They are not anywhere as laboratory standard nor highly stable as platinum resistance thermometers. Eli's comment which they let through