21 K band(21=30 GHz) and optional 14 V band (51-59 GHz) microwaves of water vapour and oxgen. It is called as brightness temperature. sun as black body radiator is to be avoided
Theory of operation
Temperature profiles can be obtained by measuring the radiation intensity, or brightness temperature, at points along the side of the oxygen feature at 60 GHz. By sampling the brightness temperatures outward from line center, where the opacity is so great that all signal originates from the atmosphere close to the antenna, on to the “wing of the line,” where the radiometer “sees” further into the atmosphere, the instrument can obtainaltitude information. Emission at any altitude is proportional to local temperature and density of oxygen; thus the temperature profile can be retrieved.
Water vapor profiles can be obtained by observing the intensity and shape of emission from pressure broadened water vapor lines. The line near 22 GHz is suitable for ground based profiling in relatively moist areas. The emission from water vapor is in a narrow line at high altitudes and is pressure broadened at low altitudes. The intensity of emission is proportional to vapor density and temperature. Scanning the spectral profile and mathematically inverting the observed data can therefore provide water vapor profiles.
Limited resolution cloud liquid water profiles can be obtained by measuring the contribution of cloud liquid water to atmospheric spectral features of varying opacity. Cloud liquid information in the 22 to 30 GHz and 51 to 59 GHz bands is used by the MP-3000A radiometer to produce a liquid profile. Cloud base altitude information derived from the optional IRT improves the water vapor and liquid water profile retrievals.
The absorption of the atmosphere in the vicinity of the assemblage of oxygen lines centered at 60 GHz at sea level and at 4 km is shown in Figure B-2. Pressure broadening smears the numerous oxygen lines into one broad feature. The 22 GHz water vapor line exhibits similar pressure broadening.
rainfall nowcast:
SWIRLS by tracking of radar echoes to generate motion fields for extrapolation of rainfall areas in the following few hours.
SWIRLS uses data primarily from the weather radar in Tai Mo Shan (TMS), which is sited on a
hilltop at 968 m above mean sea level with unobstructed view in almost all azimuths. The radar is an S-band radar operating at a frequency of 2.82 GHz, pulse widths of 1.0 and 2.0 μs, and antenna beam width of 0.9°.
Another radar, at about 583 m above mean sea level on top of another hilltop named Tate’s Cairn, serves as a backup. The Tate’s Cairn radar has a transmitter frequency of 2.92 GHz,
pulse widths of 1.0 and 2.0 μs, and antenna beam width of slightly less than 1.0°. Basic radar data processing, including removal of ground clutters, are handled by the IRIS software [17].
Both radars complete a volume scan every 6 min. Radar data and imagery are generated based on a composite of the two radars with Tai Mo Shan radar being the primary source. SWIRLS is configured to process radar data immediately upon reception of radar data, and thus also runs once every 6 min.
Dual polarised S band doppler radar 雙偏振多普勒雷達in HKO Tate Cairn, facebook since 2015
rainfall nowcast by optical flow technique in HKO
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