NUMBER 57

DATE: 05/05/88

Sector Processing Center (SPC):

During March, NOA, ESA, CSU and JMA collectively processed greater than 86% of A data into B1 and/or B2 data.

Normal operations were reported by NOA, ESA, JMA, and CSU.

AES reported a major crash of both its new optical disk archival system and its tape system; this caused the loss of almost 60% of the B3 data for March 1988. These systems have been restored. Past collection rate reports for AES included only the success in obtaining the primary target images; however, a back-up procedure has been in place to obtain a later image if the primary image is missed (something all the SPCs do). Combining the number of primary and back-up images (including partial images) raises the AES collection rates to 68% (Apr 87), 71% (May 87), 68 (Jun 87), 85% (Jul 87), 94% (Aug 87), 93% (Sep 87), 94% (Oct 87), 90% (Nov 87), 93% (Dec 87), 89% (Jan 88), 87% (Feb 88), and 41% (Mar 88).

JMA reported the delivery of the missing navigation parameters for the B1 data in June 1984. These parameters were missing because they are not usually calculated when a large portion of the image is missing; during June 1984, the malfunctioning scan mirror limited image coverage to the northern hemisphere.

CSU reported some problems with GOES-6 in March which caused the loss of some data.This was the scanner "sticking" problem (reported previously), which caused the loss of the southern portion of the image for the early part of March.

Special Area Processing Center (SAPC):

No reports were received.

Satellite Calibration Center (SCC):

No report was received.

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.

GOES-6 B3 data for November 84 through January 85 have been delivered to the ICA.

The GPC has received the replacement navigation information for June 84 for GMS; these data are being processed now. After a check of the quality of the navigation, they will be sent to the ICA. The calibration for the VIS channel B3 data in early July 84 has been corrected; these data will also be shipped after quality checks.

The replacement NOAA-8 B2 data set for June 84 has not yet been received from NOAA.

NOAA-9 B3 production has been completed through April 87 and is continuing. Replacement NOAA-9 B2 tapes for June and July 86 have been received and processed. The declining sensitivity of the VIS channel is readily apparent over the two year record; a preliminary estimate of the rate of decline is about 7-8% per year. This decline rate is being determined for all sub-targets used in our analysis to select the best estimate of this rate. W. Staylor, at NASA Langley, has been independently monitoring the relative calibration of the NOAA VIS data using the Libyan desert as a target. Comparison of our results for the same target shows excellent agreement. We are also using the results of the routine QC calculations to test for any trend in the IR calibration over the whole NOAA B3 data set. Upon selection of the best estimate of the relative calibration changes, the NOAA-9 B3 data tapes will be processed to remove any calibration trends. Delivery of NOAA-9 B3 should begin towards the end of May.

Comparison of the calibration monitor results for October/November 86 with the aircraft calibration obtained during the FIRE Cirrus Intensive Field Observations is still underway. This comparison has now been augmented by the addition of the results of W. Staylor, discussed above, the results of several indirect calibrations, especially those performed by C. Gautier using White Sands as a target, and additional aircraft data from late 1985 and early 1988. The results of C. Gautier are for GOES-4, 5, and 6, as well as NOAA-7 and 9; hence, the ratios of GOES to NOAA can be compared to the SCC results. Thus, we have two independent determinations of the normalization of GOES to NOAA, two independent determinations of relative trends of each NOAA satellite and the ratios between them, and several absolute calibations of the NOAA radiometers from aircraft flights over the past four years. Combining the trend information with the individual aircraft measurements confirms the trends determined with the satellite data and, therefore allows the aircraft data to be intercompared. Combining the different ratio determinations also confirms the detailed time histories of the calibration of GOES. The result of all this is a set of consistent measurements that determine a single absolute calibration for the NOAA-9 AVHRR Channel 1; the results appear to be consistent to within 5%. Some further work is needed to refine the interpretation of these data; this should be completed by the end of May.

The exciting prospect presented by this combined result is the establishment of an absolute radiometric calibration for all of the following radiometers: AVHRR on NOAA-6, 7, 8, and 9; VISSR on GOES-4, 5, 6, and 7 and on GMS-1, 2, 3; and the radiometer on METEOSAT-2 (which can be extended to METEOSAT-1). The key role of the ISCCP effort is the normalization of all of the geosynchronous satellites to the polar orbiters and the monitoring of the relative behavior of the whole series of polar orbiters. Papers are being prepared to report these results.

Digital sea ice data for 1985 and 1986 have been ordered from NOAA; delivery is expected this month. Availability of later data is scheduled as follows: 1987 Arctic sea ice data will be ready in August of this year, 1988 Arctic data will be completed by August of 1989, and Antarctic data for 1987 and 1988 will be completed in August of 1989. The production of sea ice data is scheduled to be operational by the end of this year; hence subsequent data sets (for 1989 and beyond) should be available in near-real-time.

The replacement TOVS data for three months during the period from July 83 to January 85 have been received and processed. Additional quality checks (comparisons of several temperature/humidity climatologies) did not suggest any need for further data editing. The TOVS data for 1983 and 1984 will be delivered to the ICA as soon as the tape format is verified and the documentation revised.

The addition of a quality test to the processing of the TOVS water vapor data (described in the last report) did improve the surface temperature retrievals somewhat; however, we also discovered that most of this problem is related to numerical inaccuracies when the water vapor opacity is so large that little information concerning the surface is actually contained in the satellite observation. This occurs in the tropics, especially for large satellite zenith angles. This problem has been resolved; production of the current version of C1 data for July 83 and January 84 is almost complete.

The absolute calibration that has been determined for the AVHRR Channel 1 appears to be about 30% (relative) higher than the calibration adopted for ISCCP. Remember that the ISCCP calibration is the pre-launch calibration for NOAA-7 and that all that was done to check it was to see if the retrieved surface reflectances were consistent with literature values. The key surface reflectance is that of North Africa, since the brighter ice surfaces of Greenland and Antarctica correspond to darker radiances at their lower solar zenith angles and a gain change does not affect the darker surfaces much. The adopted calibration seemed a little dark (i.e., the mean reflectance of North Africa is about 30%), but no definitive decision was possible, given the range of values reported in the literature for various portions of North Africa. The uncertainty was stated to be about 10%, absolute. If the new absolute calibration is adopted, then the reflectance of North Africa will be increased by about 9%, absolute, still consistent with the estimated uncertainty.

Such a large change in the VIS calibration will significantly alter the cloud optical thickness values reported by ISCCP. Since a definitive value for the calibration should be available by the end of May, we have decided to delay the delivery of C1 data until this calibration is available. This also gives us time to check the IR calibration more carefully. Processing of the C1 product will commence in early June. The special data sets for the ISCCP Polar Cloud Workshop and for the FIRE project can, however, be produced now with the current calibration. This is, in fact, a better strategy so that the ISCCP products are comparable to analyses of other researchers in these two experiments, who also used the nominal NOAA-7 calibration.

The C data production schedule is as follows:

for May

1. NOAA-7 data for January and July 1984 for the Polar Workshop 2. NOAA-9 data for October and November 1986 for FIRE CIRRUS 3. NOAA-9 data for July 1987 for FIRE MARINE STRATUS 4. GOES-6 data for October and November 1986 for FIRE CIRRUS

for June

1. complete the FIRE data sets 2. C1 data for all satellites for July 1983 and January 1984

for July

1. C1 data for all satellites for August 1983 and April 1985 2. GOES-6 data for July 1987 for FIRE

For August and following months, we will produce two months of C1 data per month in sequence from September 1983 onwards.

The production of the GOES-6 data for FIRE in July 1987 will be delayed until our B3 production software is changed to accommodate the new CSU format that was implemented in April 1987, when NOAA changed the transmission format for GOES data.

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, GOES-6, GOES-7, NOAA-9 and NOAA-10 remained good. The intermittent power and attitude control problems on NOAA-9 have not recurred. Continuing problems with the AVHRR on NOAA-H have now delayed its launch until at least August 1988.

Obtaining NOAA-10 B1/B2 data over the Indian sector starting in December 1986.

Arranging for the delivery of INSAT B1 data.

Completing BC data for 1987.

Delivering all B3 data for 1985 and 1986.

Delivery of special C data sets for the polar workshop, FIRE, the WGNE, and ERBE.

Beginning delivery of the final version of C1 data.