[A-CG41] Satellite Earth Environment Observation

[ACG41-P04] Development of a 300-GHz ground radiometer to improve the accuracy of water vapor estimation and its inversion

*Tamura Ryosuke¹, Nawo Eguchi², Kentaro Araki³, Masatomo Harada¹ (1.Japan Aerospace Exploration Agency, 2.Research Institute for Applied Mechanics, Kyushu University, 3.Meteorological Research Institute)

Keywords:remote sensing, radiometer, 300GHz, inversion

It has been noted that monitoring water vapor from the surface to 1 km is important to understand and predict the life cycle of severe weather events. Remote sensing technique with a ground-based microwave (MW) radiometers is one of the efficient way to get the vertical structure of water vapor and air temperature with high temporal resolution. The Japan Meteorological Agency (JMA) has deployed ground-based MW radiometers to monitor the inflow of water vapor that causes severe rainstorm. The relationship between radio wave frequency and the intensity of absorption and emission by water vapor is related to the relative sensitivity to its vertical altitude. In other words, ground-based observations with the terahertz (THz) band (above 100 GHz), where the effect of absorption and emission by water vapor is stronger than in the MW band, are characterized by relatively strong sensitivity to water vapor in the lower atmosphere. Our numerical experiments with the U.S. Standard Atmosphere as a profile have shown that the accuracy of estimated water vapor in the lower atmosphere (below 2 km altitude) can be improved by about 10% when a 300 GHz THz radiometer is used together with a MW radiometer, compared to observations with a MW radiometer alone. In addition to numerical studies, the development of a 300-GHz ground radiometer has also been underway. We have designed and tested a 300-GHz receiver and constructed a ground radiometer system which is expected to achieve an observation accuracy of 1.0 K around 300GHz.
In the middle of February 2025, we are currently planning an observation with our 300 GHz THz radiometer to demonstrate the results of the numerical experiment suggesting that the addition of 300 GHz observations will improve the accuracy of water vapor estimates in the lower atmosphere. For our first demonstration, the 300-GHz THz radiometer will be put beside a MW radiometer (Radiometrics Model MP-3000) on the observation point of Meteorological Research Institute (MRI). Our schedule includes the release time of a radiosonde, which daily released at 9:00 JST (0:00 UTC) from Aerological Observatory about 200 m away from the MRI. In the analysis of the observation data, the water vapor profile estimated from the brightness temperature of the radiometers will be compared with the radiosonde data. Then we will evaluate the improvement of accuracy owing to the THz radiometer.