NUMBER 115

DATE: 03/05/93

Sector Processing Center (SPC):

During January, NOA, JMA, AES, CSU and ESA processed greater than 90% of A data into B1/B2 data.Normal operations were reported by NOA, JMA, AES, CSU and ESA.ESA reported the beginning of a shift of METEOSAT-3 to 75W to complement the GOES-7 coverage better.AES shipped B2 data for March 92 to the GPC; only April, May and June 92 data are still to be shipped.

Special Area Processing Center (SAPC):

No report received.

Satellite Calibration Center (SCC):

The SCC received AC data for November 92 from NOAA-11 and for January 93 from GMS-4 and GOES-7. BC data for METEOSAT-3, METEOSAT-4 and GOES-7 for October 92 were sent to the GPC this month.

Global Processing Center (GPC):

The GPC continued to receive B2 data, BC data and correlative data in a routine manner.Production of NOAA-11 (preliminary) B3 data is current.Production of NOAA-12 (preliminary) B3 data is current.Production of METEOSAT-4 (preliminary) B3 data is current.Production of METEOSAT-3 B3 data has not started yet.Production of GOES-7 (preliminary) B3 data is current. The B2 data delivery backlog includes April - June 92.Production of GMS-4 (preliminary) B3 data is current.Production of all INSAT-1 (preliminary) B3 data has been completed. INSAT-1 B3 have been re-calibrated for January 86 - December 87. Tests of the calibration are underway.Production of the ice/snow correlative dataset is current.Re-processing of the whole TOVS dataset has now been completed and the new data shipped to the ICA. Regular processing of TOVS resumed and has been completed through February 92. Two format changes in the delivered TOVS product have occurred, one in March 92 and the other in September 92, so that the GPC processing software will have to be modified to accomodate these changes. Beginning with September 92, the number of TOVS soundings increases dramatically; instead of selecting a subset of the soundings from two satellites as before (representing about 25-50% of the total data), NOAA is now processing all of the soundings. The current frequency of TOVS data within the C1 dataset is once daily; however, this frequency will be re-evaluated to see if it is now possible to obtain several-times daily coverage.Production of CX/C1 data for INSAT has commenced. These first results will be used to test the INSAT radiance calibrations by comparisons with overlapping measurements by NOAA, METEOSAT and GMS satellites.A technique to improve polar cloud optical thickness retrievals has been developed. The problem is that, when the surface reflectance is high and nearly isotropic as for snow and ice, the larger anisotropy of cloud reflectance can produce situations where a low optical thickness cloud can appear darker than the clear scene, especially for high solar zenith angles. This condition produces two possible solutions for a particular visible radiance in some viewing geometries. In the ISCCP analysis, there was no way to remove this ambiguity, so the larger optical thickness value was always selected. However, the reflectivity of snow and ice surfaces at 3.7 m wavelength is much lower (because they are composed of much larger particles) and the reflectivity of clouds is generally (though not always) higher than that of a snow and ice surface. Hence, the 3.7 m reflectivity distinguishes between the low and high optical thickness solutions (usually these two values differ by almost an order of magnitude). The new analysis uses the 3.7 m reflectances to choose which solution will be retained. The results of the new method are being compared with theoretical calculations and some actual observations of cloud optical thicknesses in the Arctic.

ISCCP Central Archive (ICA):

The ICA continued to receive B1 data from NOA, AES, ESA, CSU and JMA and B3 and C data from the GPC in a routine manner.

The GEWEX Science Steering Group and the JSC/CAS Working Group on Radiative Fluxes met in San Diego in early February. Discussion of ISCCP concerned three major topics: (1) current status of data processing and validation, (2) plans for re-processing the data products to make improvements, and (3) possibilities for enhancements of ISCCP during the GEWEX era (95 and onwards). Key validation results are as follows. (1) Although the radiance calibrations appear to be within the estimated uncertainties (about 10% for visible and 5% for infrared), the largest errors appear as systematic shifts that occur when the reference polar orbiter is changed. (2) Cloud amounts appear to be accurate to about 7%, but amounts over land (particularly in winter) are underestimated. (3) Polar cloud amounts appear too low by about 15-20% in summer and 5-10% in winter. (4) Cloud optical thicknesses and top temperatures appear to accurate to within 10% and 3K, respectively, based on comparisons with results from field experiments. (5) The exception is thin (optical thicknesses less than about 4) ice clouds, where the optical thicknesses are biased high by 50-100%; consequently, cloud top temperatures are biased high by about 6-10K.Results of field experiments, like FIRE and ICE, as well as continuing studies of cloud detection in the polar regions, form the basis for making improvements in the ISCCP analysis to correct some of the problems found in the validation studies. Moreover, research use of the ISCCP data products has highlighted some useful changes that could be made in the cloud type information reported. Therefore, plans were presented for a complete re-processing of the ISCCP data products to make these changes: the current version of the C1/C2 data would be terminated at June 91 and the new version would be completed in about one year. Both groups endorsed these plans with emphasis on three points: (1) refinement of calibration is to be based on continuing ISCCP investigations, (2) cloud type information should be expanded to make the ISCCP results more useful for cloud dynamics research, and (3) the pixel-level results (Stage CX data) should be archived as an ISCCP data product to support cloud process studies.Possible future enhancements of the ISCCP processing were discussed. Current plans of the agencies that operate meteorological satellites indicate that one new spectral channel will become common to the whole constellation by 95 (if HIRS data from the polar orbiters is combined with AVHRR), namely a 6.7 m channel. Enhancements that may be feasible are: (1) enhanced cirrus detection using 6.7 m channel (possibly 3.7 m and split-window on AVHRR), (2) retrieval of cloud particle size using the 3.7 m channel on AVHRR (later the 1.6 m channel), (3) adding a combined AVHRR/HIRS/MSU analysis, (4) combining the analysis of ISCCP and SSM/I datasets, which could be extended to include a combined AVHRR/HIRS/AMSU-A/AMSU-B analysis, and (5) merging information from various surface observations (lidars, ceilometers, rawinsondes) of cloud base locations with ISCCP to provide improved cloud vertical structure information. It was noted that most of these ideas are presently being studied by several research groups.

The health of GMS-4, METEOSAT-3 (now at 75 W), METEOSAT-4, METEOSAT-5, GOES-7, NOAA-11, and NOAA-12 remained good. Launch of GOES-I is now scheduled for April 94.

Stage B3: July 83 - June 91Stage CD: July 83 - December 91Stage C1: July 83 - June 91Stage C2: July 83 - June 91

Delivering the backlog of GOES-7 B1/B2 data for April, May and June 92 to the GPC.

Delivery backlog for B3 data = 13 months (with respect to planned schedule). B3 data for 96 months have been archived.

Delivery backlog for C1/C2 data = 13 months (with respect to planned schedule). C1 data for 96 months have been archived.