Initial Assessment of the First Results of Sensing the Lower Troposphere with COSMIC-2
Presenter:
Sergey Sokolovskiy
University Corporation for Atmospheric Research
University Corporation for Atmospheric Research
Talk
The FORMOSAT-7/COSMIC-2 (hereafter COSMIC-2) Global Navigation Satellite System (GNSS) Radio Occultation (RO) receivers use high gain antennas with beam forming to achieve the highest possible Signal to Noise Ratio (SNR) at all azimuths. This is aimed mainly at improving retrieval quality in the moist lower troposphere. The COSMIC-2 receivers acquire signals from two GNSSs, GPS and GLONASS, and track all RO signals in full model-aided open-loop (OL) mode. First, as was shown theoretically and confirmed using COSMIC GPS RO signals, deep OL tracking (down to -350 km of the height of straight line) allows detection of the tropospheric ducts which exist on top of the boundary layer (this is useful for data quality control and assimilation). While this detection was marginally possible with the SNRs observed from COSMIC, we expect it to be more robust with the higher SNRs from COSMIC-2. Second, while some of the lower troposphere RO biases (like those induced by ducts or propagation through random refractivity irregularities) are not fundamentally related to the SNR in the sense that they would exist even without the noise, other biases (like those related to the impossibility to distinguish RO signals from noise by either truncating too high or inverting RO signals heavily mixed with noise) are fundamentally related to noise and those biases are expected to be reduced with the increased SNR. Third, we will compare quality of the GPS and GLONASS occultations in the lower troposphere where GLONASS potentially may result in: (i) reduced loss of the SNR related to OL range mismodeling (due to larger code chip length), and (ii) reduced cross-satellite interference (due to frequency division). We will present initial assessment of COSMIC-2 performance in the moist lower troposphere by discussing all aspects above and illustrating them with the first results of COSMIC-2 data processing.
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