MWRnet is a network established in 2009 of scientists working with ground-based microwave radiometers. It would contain a network of 16 aethalometers, 12 sky radiometers and 12 nephelometers. By the 2010s four microwave radiometers have been flown on interplanetary spacecraft. They are used in meteorology to measure solar radiation as pyranometers, pyrheliometers and net radiometers. This instrumentation included IGY radiometers, receivers, radar, and optical equipment. In following years a wide variety of microwave radiometers were tested on satellites. Most radiometers for remote sensing (RS) acquire multispectral images. Microwave radiometers operate in the microwave wavelengths. Infrared and/or ultraviolet radiometers may have been included. The receivers are polarization-sensitive differential radiometers measuring the difference between two telescope beams. Analysis showed inadequate thermal shielding of the sensor's radiometers due to excessive heating at perihelion. In infrared thermography, the radiation is detected and measured with infrared imagers (radiometers). Spectrometers and radiometers are made for measurement of UV radiation. Usually, Earth observation satellites have three or more radiometers. A series of radiometers were launched on satellites from the 1970s to the 2000s.