ALBERT

Beschreibung: The first copy of the SSMIS (Special Sensor Microwave/Imager/Sounder) was launched on board the DMSP (Defense Meteorological Satellite Project) F-16 satellite in October 2003. During March-April 2004, six 5-hour SSMIS under-flights were conducted with the CoSMIR on board the NASA ER-2 aircraft over the coastal region of California. CoSMIR has nine channels at the frequencies of 50.3, 52.8, 53.6, 91.665 (V and H polarization), 150, 183.3+/-1, 183.3+/-3, and 183.3+/-6.6 GHz. All except the two 91.665 GHz channels are horizontally polarized. The instrument was carefully calibrated with LN2 target in the laboratory before the flights. Three of the aircraft flights passed over Lakes Pyramid and Tahoe that could be used to validate the in-flight sensor calibration. Immediately after these flights, an inter-comparison of the calibrated SSMIS and CoSMIR brightness temperatures (T(sub b)) followed. The results showed that, for channels at frequencies 〉 or equal to 91.665 GHz, the SSMIS and CoSMIR T(sub b) values tracked each other very well; for some channels there were some bias with magnitude generally less than 3-4 K (SSMIS values were higher). For the three 50-54 GHz channels, the SSMIS T(sub b) values were higher and frequency-dependent. For the least opaque channel at 50.3 GHz, the SSMIS T(sub b)'s over the ocean surface were higher than those of CoSMIR by more than 20 K under the clear-sky conditions. The most plausible explanation for this to happen is to assume that the 50-54 GHx channels of the SSMIS are vertically polarized. This assumption appears to be consistent with independent radiative transfer calculations. Attempts to estimate vertically polarized radiometric responses for 50-54 GHz channels of the SSMIS based on the CoSMIR observations are not plausible and results not reliable because of the highly variable ocean surface conditions (e.g., wind-induced emissivity changes). A conversion of the CoSMIR 50-54 GHz channels from horizontal to vertical polarization, and a subsequent repetition of the SSMIS under-flights are the right approach for the calibration/validation of the 50-54 GHz channels of the SSMIS. Details of the SSMIS-CoSMIR inter-comparison will be presented.

Beschreibung: In this paper we explore the application of combined millimeter-wave radar and radiometry to remotely measure snowfall. During January-February of 2003, a field campaign was conducted with the NASA P-3 aircraft in Wakasa Bay, Japan for the validation of the AMSRE microwave radiometer on board the Aqua satellite. Among the suite of instruments-on board the P-3 aircraft were the Millimeter-wave Imaging Radiometer (MIR) from the NASA Goddard Space Flight Center and the 94 GHz Airborne Cloud Radar (ACR) which is co-owned and operated by NASA Jet Propulsion Laboratory/University of Massachusetts. MIR is a total power, across-track scanning radiometer that measures radiation at the frequencies of 89, 150, 183.3 +/- 1, 183.3 +/- 3, 183.3 +/-7, 220, and 340 GHz. The MIR has flown many successful missions since its completion in May 1992. ACR is a newer instrument and flew only a few times prior to the Wakasa Bay deployment. These two instruments which are particularly well suited for the detection of snowfall functioned normally during flights over snowfall and excellent data sets were acquired. On January 14, 28, and 29 flights were conducted over snowfall events. The MIR and ACR detected strong signals during periods of snowfall over ocean and land. Results from the analysis of these concurrent data sets show that (1) the scattering of millimeter-wave radiation as detected by the MIR is strongly correlated with ACR radar reflectivity profiles, and (2) the scattering is highly frequency-dependent, the higher the frequency the stronger the scattering. Additionally, the more transparent channels of the MIR (e.g., 89, 150, and 220 GHz) are found to display ambiguous signatures of snowfall because of their exposure to surface features. Thus, the snowfall detection and retrievals of snowfall parameters, such as the ice water path (IWP) and median mass diameter (D(me)) are best conducted at the more opaque channels near 183.3 GHz and 340 GHz. Retrievals of IWP and D(me) using the MIR measurements at 183.3 and 340 GHZ are currently in progress, and the results will be compared with those derived from the ACR reflectivity profiles. Implication from this comparison will be discussed.

Beschreibung: A rich dataset was obtained with observations from the MIR (Millimeter-wave Imaging Radiometer, 89, 150, 183.3$\pm$1, 183.3$\pm$3,183.3$\pm$7, and 220 apprx.GHz), the AMPR (Advanced Microwave Precipitation Radiometer, 10.7, 19.35, 37, and 85 approx. GHz), and the EDOP (ER-2 Doppler Radar, 9.6 approx. GHz) on board the ER-2 aircraft during the CAMEX-3/TEFLUN-B (Convection and Moisture Experiment/Texas and Florida Underflights) TRMM (Tropical Rainfall Measuring Mission) field campaign. Measurements over the ocean from these three instruments on 26 August 1998 were used in our iterative retrieval algorithm to estimate hydrometeor drop size profiles, The algorithm attempts to minimize the difference between the observations and forward radiometer and radar calculations based on the estimated profile. The high frequency MIR observations provide detailed information about the high altitude ice microphysics, while the AMPR is mostly used to define liquid hydrometeor characteristics. The EDOP provides an initial estimate of the profile and as a consistency check throughout the iterative cycle. The retrieval algorithm, specific results for convective and anvil cases, and general implications of this work will be presented.