NUMBER 48

DATE: 08/07/87

Sector Processing Center (SPC):

During June, ESA and JMA collectively processed 95% of A data into B1 and/or B2 data.

Normal operations were reported by ESA, JMA and NOA. The March and April monthly reports were received from NOA, but no processing matrices were included. No data processing report was received from CSU.

NOAA delivered two more months of NOAA-8 data for March and April 1984, leaving only two months undelivered.

ESA reported the loss of about 24 hr of data on June 29 and 30 due to a fault in the ground communications between the receiving station and ESOC. This condition has been corrected.

CSU reported that a simulation of the old GOES IR translation table would be employed to process B2 data through July, the end of the FIRE Marine Stratus experiment. In September the new 10-bit to 8-bit translation table will be implemented. No B2 data have been delivered since March 1987. CSU also reported that GOES-6 transmissions will include two additional IR channel images, starting 6 August 1987; however, CSU cannot begin collection of these extra images immediately. (The status of GOES-7 transmissions is not known.)

AES reported significant disruptions of operations in June. The receiving and computing equipment was moved in mid-month and numerous electrical storms occurred. A new staff, that was not completely familiar with the system, made recovery under these unusual conditions more difficult. Planning has been completed to by-pass the complex data receiving and processing system that is "upstream" of their system, which should significantly reduce data losses. Other software weaknesses are also being corrected. Improved performance should be obtained over the next few months.

Special Area Processing Center (SAPC):

No reports were received.

Satellite Calibration Center (SCC):

The GPC received BC data from the SCC for January 1987 for METEOSAT-2, October 1986 and January 1987 for GMS-3, and for October 1983, July and October 1985, and April 1986 for GOES-6. Preliminary results were also received for January 1986 for GOES-6. Results from more extensive comparisons of the calibrations of both the VIS and IR channels of NOAA-7 and NOAA-9 using METEOSAT-2 and GMS-3 were delivered.

Global Processing Center (GPC):

The GPC continued to receive B1 and/or B2 data from JMA, ESA, CSU, AES and NOA and correlative data from NOAA/NESDIS in a routine manner.

The normalization of the NOAA-7 and NOAA-9 visible channel calibrations has been repeated to insure that the filtering process, used to isolate clear radiances, had not introduced any bias. These results produced the same normalization coefficient; however, the quality of the regression between the global maps obtained from NOAA-7 and NOAA-9 was improved. The final relationship between the NOAA-7 and 9 VIS calibrations, obtained by the GPC using three weeks of overlapping global data, is intermediate between the two values obtained by the SCC. The SCC results give relationships of

VIS(NOAA-9) = 1.18 VIS(NOAA-7) + 0.004 from METEOSAT-2

and

VIS(NOAA-9) = 1.06 VIS(NOAA-7) + 0.010 from GMS-3.

These differences may be caused by the small differences in the spectral responses of the three radiometers and the non-linear effects of data range discussed at the Working Group meeting. In any case these three values agree to within 2% at the mid-point of the radiance range. The relation adopted is that from the GPC results:

VIS(NOAA-9) = 1.13 VIS(NOAA-7).

Since the comparison of the NOAA-7 and 9 IR calibrations obtained by the SCC shows no difference greater than the difference between the METEOSAT and GMS results ( 1K), no normalization change in the NOAA-9 calibration for IR will be made.

An minor error in the calculation of the seasonal variation of the solar constant in the GPC AVHRR calibration monitor has been discovered. This error does not affect the monitoring of the NOAA calibrations or the NOAA-7 to 9 normalization, but it does change the magnitude of the apparent seasonal cycle seen in the NOAA-7 results. The entire monitor run for the 19 months of NOAA-7 data is being repeated to improve the accuracy of the solar zenith angle models derived from this data set.

Production of GOES-6 B3 data has been completed through January 1985. Routine production included the QC procedures from August 1984 through January 1985. Elimination of the QC backlog for July 1983 through July 1984 has also begun; three months of data have already been processed for GOES-6. The GOES-6 B3 data from August through October 1983 are now being processed (changing the calibration tables to include the new BC values) for delivery to the ICA.

Inspection of the navigation accuracy of the GOES-6 data during orbital maneuvers, which began in late 1984 to shift the satellite's position to optimize seasonal storm observations, has been completed for the first two moves. Errors are very large (as much as 30 B3 pixels) at the time of the beginning or ending of a position shift; these errors persist for about one day and then are eliminated. No corrective action is planned; these images will be flagged as incorrectly navigated but not eliminated from the B3 data set.

Further inspection of GMS B3 data for July 1983 and January 1984 reveals a 1-2 pixel error which seems constant, even though our latitude-longitudes agree with those provided by JMA for 121 reference points. Since a systematic error is probably due to a code error, this does not appear to be a serious problem. The final version of the GMS B3 production code is being tested.

Progress has been made on the completion of several ancillary and correlative data sets. The topography data set, to be used in the cloud algorithm and supplied on the C1 data tapes, has been constructed and quality checked. The sea ice data map grid and format have been designed and the processing algorithm completed; re-mapping of the ice data will begin next week. These data will be merged with the snow data set for use with the cloud algorithm. Testing of the TOVS error and retrieval codes is nearly completed and a new format, compatiable with the C1 data format, has been designed.

The major planned changes to the cloud detection step of the algorithm have been implemented: a refinement of the clear sky logic to test the 5-day and 30-day maximum temperatures for cloud contamination or bad data, the development of a regional estimate of the difference between the maximum temperature and the mean clear sky temperature, and the introduction of a process to compare clear sky visible reflectances by surface type (ocean, land, vegetation, ice, snow). These changes must now be refined by testing. A crucial test is the comparison of the clear sky radiances obtained with and without these refinements to insure that the desired improvements have been obtained without introducing any new difficulty. Special emphasis will be given to summer and winter comparisons and to testing of algorithm sensitivity in the polar regions.

In order to provide a comprehensive set of test cases, the "old" algorithm is being applied to the January 1984 data set (with no normalization for GOES-6 data and no NOAA-8 data). The production of this additional C1 data set will be completed later this month and delivered to the ICA for preliminary research use.

Further testing of the radiation procedures has led to the development of an improved method of interpolating the IR radiances from the model to the specific satellite zenith angle for each pixel. The results from this analysis are also being used to develop an improved viewing geometry correction procedure for the IR radiances in the cloud detection step. This procedure is not actually needed for the analysis of the geosynchronous satellite data, but is crucial to the analysis of the polar orbiter data, especially in the tropics.

The minor changes to the C1 contents and format have been completed. Revisions to complete the separation of the VIS-channel dependent results are underway.

The entire production system is being revised to optimize performance; these changes are being tested during the production of the C1 data for January 1984.

A complete revision of the B3 data documentation was mailed to WMO in early July.

ISCCP Central Archive (ICA):

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

The health of GMS-3, METEOSAT-2, NOAA-9 and NOAA-10 remained good. VIS channel 5 on GOES-7 experienced a sudden 70% increase in gain on 16 July 1987. Investigation of this change has not found a reason as yet. Data from channel 4 are being used in place of the channel 5 data, a change which is transparent to the user. The third encoder lamp (of four) on GOES-6 is showing signs of failure; the voltage was increased to step 4 on 10 July 1987. In order to stretch out the life of the third and fourth lamps until a replacement satellite can be launched (not before late 1989), the GOES-6 images are being truncated at line 1400, about 35S. However, when this procedure was implemented in early July, a build-up of lubricant on the scan gears occurred; thus, every three hours (the ISCCP time slot), a complete image will be collected. Even with this procedure, the expected lifetime of GOES-6 is now estimated to be through 1988. As reported at the Working Group meeting by ESA, the orbital inclination of METEOSAT-2 will no longer be controlled in order to conserve the remaining fuel until the replacement satellite is launched. Resumption of Ariane launches is expected early next year.

Delivery of NOAA-8 B2 data for May 1984 and June 1984.

Delivery of BC data for GOES-6 for January 1984 through July 1984 and for January 1985 and January 1986.

Normalization of NOAA-8 AVHRR to NOAA-7.

Delivery of GMS B3 data for August 1983 through January 1985.

Delivery of B3 data for 1985 and 1986.

Obtaining NOAA-10 data over the Indian sector starting in December 1986.

Arranging for the delivery of INSAT B1 data.