Performance assessment of an LNA used as active cold load

The EMIRAD-2 radiometer is an airborne radiometer, which has been developed for calibration and validation of the ESA/SMOS mission data, as well as for data collection for development and evaluation of models for parameter retrieval, based on radiometric L-band data. The instrument has been applied in various campaigns in very different environments. Primary calibration sources are a traditional hot load along with a noise diode, and the calibration quality is verified prior to almost each flight using a liquid Nitrogen cooled target. EMIRAD-2 also features a commercial-off-the-shelf (Miteq) low noise amplifier (LNA), operated as an active cold load (ACL). This paper shows results for the ACL performance throughout several years of operation under very different conditions, and important parameters, such as stability, repeatability, and sensitivity to operating temperature variations are assessed.