beam/radiation pattern: The directional dependence of radiation power from the antenna (transmit) or as received by the antenna (receive).

bolometer: An instrument that measures incident electromagnetic radiation.

cross-frequency mitigation: The process of measuring a particular band by splitting it into sub-bands (spectral analysis) and then looking “across the frequencies” for outlier channels. These outliers are presumed to be contaminated with RFI because they have more power in them than would be expected.

direct data assimilation (DDA): A powerful technique developed during the past two decades. DDA optimally uses all available data from satellites, balloons, radars, and surface stations to steer numerical weather prediction (NWP) models. DDA applied to satellite data is known as direct radiance assimilation (DRA) and accounts for most of the improvements in the performance of NWP models in the Southern Hemisphere where other sensors are scarce.

downwelling: Natural radiation that radiates down from the sky.

Environmental Data Record (EDR): Characteristic information regarding an environment that has been observed: once an Earth remote sensing observatory collects incident radiation and it is sent to researchers for processing, the researchers organize the data and interpret them to produce EDRs. EDRs include sea and land wind speed, sea and air temperature, precipitation, sea salinity, and soil moisture. See Table 2.1 in Chapter 2 for a complete list.

Gaussian: A frequency distribution of a variable that exhibits normality and is useful for identifying noise in an instrument.

Global Navigation Satellite System (GLONASS): A radio-based Russian geonavigation satellite constellation operated by the Russian Space Forces that is similar to the United States’ Global Positioning System.

interference: The effect of unwanted energy due to one or a combination of emission(s), radiation(s), or induction(s) on reception in a radiocommunications system, manifested by any performance degradation, misinterpretation, or loss of information that could be extracted in the absence of such unwanted energy.

interference mitigation: The process of preempting, identifying, and excising radio or microwave interference from observational data. It can be either unilateral (in the case of excising) or multilateral (in the case of coordination agreements).