Intercalibration of microwave temperature sounders using radio occultation measurements

Abstract

This is a study of the usefulness of radio occultation (RO) data for intercomparing different microwave temperature (MWT) sounding instruments. The RO data used are from the Global Navigational Satellite System Receiver for Atmospheric Sounding on the Metop-A and B satellites. The MWT sounders investigated are the Advanced Microwave Sounding Unit-A instruments on the satellites NOAA 15, 16, and 18 and Metop-A. We collocate RO and MWT data and then use these collocations to study various aspects of the MWT instruments. In addition, two different versions of the MWT data are compared: standard operational data (OPR) and the NOAA Integrated Microwave Intercalibration Approach data (IMICA). The time series of monthly mean differences shows that there are robust patterns for each satellite and data version, which mostly drift only slowly over time. The intersatellite spread, measured by the standard deviation of the yearly mean values by all satellites, is between 0.1 and 0.4 K, depending on channel, with no significant differences between OPR and IMICA data. The only notable exception is Channel 8 of NOAA 16, which appears to have a time-varying offset of 0.5-1 K relative to the other instruments. At this point it is not clear whether this deviation is real or a sampling artifact, so further study is needed. Due to the large number of collocations used, it is possible to also investigate the scene brightness and scan angle dependence of the MWT bias (relative to RO). First results of such an analysis are presented and discussed. Particularly, the investigation of the scan angle dependence is novel, since this bias pattern is difficult to assess without RO data. Further work is needed on these angular dependences, before conclusions are robust enough to include in data recalibration efforts, but our overall conclusion is that RO collocations are a powerful tool for intercomparing MWT sounders.

Assessment of NOAA NUCAPS upper air temperature profiles using COSMIC GPS radio occultation and ARM radiosondes

“…Examples, which are not exhaustive, include comparisons of versions from different processing centers [ Gorbunov et al , ; Ho et al , ], comparisons of RO to other instruments or model analyses [e.g., Das and Pan , ; Ladstädter et al , , ; Kuo et al , ], studies of ionospheric influences [e.g., Liu et al , ; Verkhoglyadova et al , ; Danzer et al , ; Mannucci et al , ], assessing RO data's utility in providing climate records [e.g., Foelsche et al , b; Steiner et al , , ], or mixes of all these and others [e.g., Gorbunov and Kirchengast , ; Foelsche et al , a; Scherllin‐Pirscher et al , , ]. The use of RO‐derived temperatures in the upper troposphere, lower stratosphere as an absolute reference has grown in recent years, as it has been used to identify radiosonde biases [ He et al , ; Sun et al ., ], evaluate model reanalyses [e.g., Kishore et al , ], and calibrate MW sounders [e.g., Ho et al , ; Zou et al , ; Isoz et al , ], in addition to evaluating hyperspectral IR sounder temperatures [ Yunck et al , ; M. Feltz et al , ]. Comparisons of COSMIC temperatures to Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer v3.5 showed agreement up to 1 K for altitudes between 15 and 40 km (~100–3 hPa) [ Olsen et al , ], while comparisons to Sounding of the Atmosphere using Broadband Emission Radiometry and Microwave Limb Sounder showed agreement over all seasons from 80°N–80°S and 100–10 hPa being under 3 and 2 K, respectively [ Das and Pan , ].…”

Interpretation of the Precipitation Structure Contained in Polarimetric Radio Occultation Profiles Using Passive Microwave Satellite Observations

“…Depending upon the sensor, these radiometers scan a wide swath and whose equivalent blackbody brightness temperature (TB) imagery can provide 3-dimensional context to the precipitation structure that is not discernable from the ROHP  observations alone. There is a large body of published work on the complementary use of RO and passive MW sounder data for radiance-level intercalibration for the Advanced Technology Microwave Sounder (ATMS) (Iacovazzi et al, 2020) and Microwave Humidity Sounder (MHS) (Isoz et al, 2015). This investigation utilizes these passive MW data in a opposite context, whereby the passive MW observations are inverted into precipitation water content profiles along the ROHP propagation ray paths.…”