| Paper: | FR-A2.4 |
| Session: | Atmospheric Applications of Radiometry II |
| Time: | Friday, March 30, 11:40 - 12:00 |
| Presentation: |
Oral
|
| Topic: |
Clouds and precipitation: |
| Title: |
Preliminary Test Flight of a Compact High Altitude Imager and Sounding Radiometer (CHAISR) |
| Authors: |
Reno K.-Y. Choi; National Institute of Meteorological Sciences | | |
| | Seunghyun Min; Satrec Initiative Co. | | |
| | Do-Youn Kim; ARA Consulting & Technology | | |
| | Tae Gyu Kim; EM-wise Communication | | |
| | Seohoon Yang; Satrec Initiative Co. | | |
| | Ho-Jin Lee; Satrec Initiative Co. | | |
| | Jongsun Park; Satrec Initiative Co. | | |
| | Sanghyun Beck; Satrec Initiative Co. | | |
| | Jong-Chul Ha; National Institute of Meteorological Sciences | | |
| | Ki-Hoon Kim; National Institute of Meteorological Sciences | | |
| | Young-Jun Cho; National Institute of Meteorological Sciences | | |
| | Sang-Won Joo; National Institute of Meteorological Sciences | | |
| Abstract: |
Three compact microwave radiometers are developed for a lightweight solar–powered HALE UAV (High-Altitude, Long Endurance; Unmanned Aerial Vehicle) or pseudo-satellite. The platform aims to operate at UTLS, i.e. altitude of 16~20 km, where air becomes thin enough to prevent operation of a conventional fossil fuel engines. Despite atmospheric science community has long been attracted in its potential scientific and operational value as an observation platform, only limited opportunities were available.
A Joint Civil-Military Committee, under Advisory Council on Science and Technology, Korea, approved a technology demonstration project for developing a HALE UAV and its applications. As one of civilian participants, NIMS (National Institute of Meteorological Sciences) is developing a payload for atmospheric observation, the Compact High Altitude Imager and Sounding Radiometer (CHAISR). The CHAISR consists of three microwave radiometers (MWR) with 16 channels between 18 and 60 GHz, radiosonde quality PTU sensors, and medium resolution visible and infrared cameras. System level design requirements for the payload required packaging those instruments within <3 kg of weight and >50 W of power consumption. Climatology shows CHAISR was expected to experience temperature as low as -75 °C and pressure up to 50 hPa at operational altitude. Even 100% of humidity through clouds. Such a harsh operational condition requirement allows neither active thermal control to protect electronic subsystems from overheating at ground or keeping them above operational temperature at the operational altitude given weight and power available. Safety considerations and contingency plans, such as payload power management and thermal control, are taken place for flawless operation with minimal user input.
Three radiometers at frequency ranges 18.325~22.425, 36.7~40.8, 49.3~60.3 GHz, respectively, are mounted on a cross-track scanning unit for spatial observation with flightline. Total weight of less than 1 kg of radiometer packages requires less than 15 W of maximum power consumption. Due to weight and power constraints, conventional onboard blackbody calibration target is not allowed. Radiometers rely on two internal references for each rotation. The scan between horizon and zenith is supposed to follow cosine response with assumption of spatially uniform atmosphere. While simultaneous measurements of noise diode provide hot reference, this widely used tipping curve calibration yields cold reference from atmospheric effect at zenith angle with cosmic background emissivity, resulting in an excellent cold calibration target at a certain scan.
Simulation of tipping curve calibration with altitude shows consistent accuracy from altitude of 8 km or above regardless atmospheric condition, for atmospherically transparent channels, i.e. less atmospheric variability above MWR. For opaque channel, comparison between horizontal and zenith measures stability of tipping curve performance. Series of verification campaigns for both ground and microflight at 5,000 ft above atmospheric boundary layer proved the method meets simulation results.
Series of preliminary flight test of the HALE UAV gave us test opportunities of CHAISR MWR at even higher altitude. In 22 and 30 September 2017, CHAISR operated at 17k and 31k ft of altitude (5.2 and 9.5 km), respectively. MWR dataset are processed with correction of operational temperature dependent signal before calculation of brightness temperature (level 1a). Tipping curve calibration take place between level 1a and lb product. Level 1x product is used as an input for retrieval process yielding vertical profiles of temperature and TPW (level 2) before comparing NWP dataset. The result shows good agreement with expectations from MWR hardware and data processing performance at all altitudes. Target altitude flights of the CHAISR onboard of the HALE UAV above troposphere are planning in near future when weather permits, hoping for next phase of the project for CHAISR to track typhoons, improved observations of weather fronts and seasonal conditions such as monsoon rains. |
