NUMBER 122
DATE: 11/04/93
Sector Processing Center (SPC):
During August and September, NOA, JMA, and ESA processed greater than 96% of A data into B1/B2 data.
In August, AES collected 100% and CSU collected 86% of B1/B2 data; in September CSU collected almost
96%.Normal operations for August and September were reported by NOA, ESA, and JMA. CSU reported
loss of data in August during a computer system upgrade; no report for September was received from AES.
Special Area Processing Center (SAPC):
No report received.
Satellite Calibration Center (SCC):
No report received.
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 GOES-7 (preliminary) B3 data is current. First examination of the replacement B2 data received from
UWS reveals an error in processing the IR images. Since the result is an image that is larger than it is
supposed to be, it may be possible to re-sample these data to recover what we need (UWS also sent the
B1 dataset, so B2 may be re-producible from that). Investigation is ongoing.Production of METEOSAT-3
B3 data has not started yet. Final testing of software has resumed.Production of METEOSAT-4/5
(preliminary) B3 data is current.Production of GMS-4 (preliminary) B3 data is current.Production of all
INSAT-1 (preliminary) B3 data has been completed. These data will not be delivered to the ICA until the
short-term calibration variations are removed.Production of the ice/snow and TOVS correlative datasets is
current.Four changes are being made to the radiative transfer model used for retrieval of cloud properties:
(1) add ice phase cloud model, (2) modify retrieval of cloud optical thickness in polar regions, (3) add IR
scattering effects for liquid water clouds, and (4) revise the continuum absorption coefficient for water vapor.
For all clouds, an ice phase microphysics model will also be used to retrieve optical thickness and top
pressure in parallel with the original liquid phase model results. The model is adapted from the work of P.
Minnis and colleagues on the FIRE research team and is consistent with available results from FIRE I and
II, ICE/EUCREX and WENPEX. The correction is only significant for a small percentage of clouds (about
5%), but produces a systematic decrease of optical thicknesses and top pressures for high, thin clouds.
Over very bright surfaces (visible albedos > 50%) in some viewing-illumination geometries, there are two
values of cloud optical thickness that are consistent with the satellite-measured visible reflectance. In the
original analysis, the larger value was always selected. However, for these same conditions, the 3.7 m
reflectance (thermal emission removed) is monotonic with cloud optical thickness, so in the new analysis,
the value of 3.7 m reflectance is used to select either the smaller or larger solution. This will significantly
reduce the average value of polar cloud optical thicknesses, but may still leave a high bias. Since the new
ice phase radiative model includes the effects of IR scattering, a correction is also made for liquid clouds
for consistency. This correction to cloud top temperatures is generally very small (1 - 2K), but does reduce
the observed systematic satellite zenith angle dependence of cloud top temperatures for lower level clouds.
Newer theoretical treatments and laboratory measurements, together with our validation studies, support
a small reduction in the water vapor continuum absorption coefficient.There have been two minor changes
in the new DX data contents: the total number of bytes has been reduced to 32 (note that the location
information for each pixel adds an additional 8 bytes) and the single "no-cloud" or "cloud" bit has been
dropped. However, the DX-READ program will calculate a cloud/no-cloud flag to provide a simple guide to
the decision.The new C1 dataset, called D1, will be changed in four significant ways: (1) some old statistics
about cloud detection and the distribution of radiances have been eliminated, (2) one new variable (Water
Path) has been added, (3) an additional optical thickness category has been added to the distribution
statistics, and (4) more cloud type information is given. The new variable is the "water path" which is
proportional to the linear average of the cloud optical thickness. Unlike the "radiatively-weighted" average
of the cloud optical thickness, which gives the proper mean albedo, this quantity is directly related to cloud
water mass. Although this variable was reported in the C2 dataset, it was calculated from the optical
thicknesses in the C1 dataset that we averaged over the map grid cell with a radiative weighting which
causes about a factor of two underestimate. The PC-TAU (cloud top pressure and optical thickness)
frequency distribution has been expanded by dividing the largest TAU category into two parts at a value near
the approximate onset of precipitation. The largest change in data contents is to add bytes that report the
spatial mean properties of several cloud types like those reported in the C2 data. This will not only increase
the accuracy of determining the monthly mean values, but give much more detailed information in the D1
dataset to examine the separate radiative effects of each cloud type. The number of cloud types (15) is
expanded to give more uniform coverage of optical thicknesses (three instead of two types for low and
middle level clouds) and to include both ice and liquid water cloud types (high clouds are always ice).Due
to renovations and construction at the GPC, the mainframe computer system was shut down from 17
September through 20 October. Although some progress was possible using workstations, most revisions
of the code only resumed last week.
A sub-group of the Working Group on Data Management met at AES in Toronto on 22 October to discuss
plans for transitioning to GOES-I after launch next year. Representatives from AES, CSU, NOAA and the
GPC were present; the SCC representative could not attend but sent comments about issues raised by the
changed characteristics of this new satellite. NOAA is considering two operational scenarios after launch
and check-out, assuming that GOES-7 is still healthy: (1) move GOES-7 from 112W to 135W and move
GOES-I to 75W and terminate METEOSAT-3 data reception (METEOSAT-3 may be replaced by
METEOSAT-5 in early 94) and (2) move GOES-7 to 135W, keep GOES-I at 90W and maintain
METEOSAT-3 (or -5) data collection at 75W until GOES-J is launched in late 94, then move GOES-I to
75W. There is disagreement within NOAA about which scenario to adopt: the first scenario risks loss of
coverage of the western sector if GOES-7 fails before launch of GOES-J, whereas the second scenario does
not provide the improved severe storm capabilities of GOES-I in the eastern sector for the 94 hurricane
season.The AES group processing GOES-7 data for ISCCP does not control when their receiving antenna
will be switched from GOES-7 to GOES-I. CSU may have the capability to collect data from GOES-7,
GOES-I and METEOSAT-3 for awhile. Software development for receiving and processing GOES-I data
is underway at CSU, but at AES software development, although started, is on hold until after GOES-I launch
next year. Therefore, it was concluded that the most likely plan is: (1) CSU assists AES in development of
new B1/B2-processing software, (2) CSU initiates collection of GOES-I, takes over collection of GOES-7
when the AES antenna is switched to GOES-I, and collects METEOSAT-3 (or -5) data if available and
possible, (3) AES begins collection and processing of GOES-I data with CSU maintaining collection of
GOES-7 until launch of GOES-J at the end of 94. Action items were for AES to firm up its plans for transition
from GOES-7 to GOES-I and for NOAA/CSU to plan on covering three satellites if scenario #2 is
adopted.The GOES-I data differ from previous GOES data in several key respects: (1) five spectral channels
instead of two (VIS = 0.55 - 0.75 m, IR = 3.80 - 4.00, 6.50 - 7.00, 10.20 - 11.20, and 11.50 - 12.50 m), (2)
radiances are quantized in 10 bits instead of 6 (VIS) and 8 (IR - changed to 10 in the AAA format), and (3)
three of the IR channels have higher spatial resolution (4 instead of 8 km). These differences raised three
questions about the ISCCP B1/B2 datasets to be produced: how many spectral channels should be
collected, what spatial sampling frequency should be used (raised with regard to B1) and how many bits
should be used to represent radiances? The answers to these questions drive data volume, primarily.
There was agreement that all five spectral channels should be collected, some argument that the B1 spatial
resolution should be increased to 4 km from 8 km, and disagreement about whether to retain 10 bit radiance
precision (requiring storage of 16 bits) or not. AES did not believe that they could handle the B1 data
volumes required to obtain either higher spatial resolution or retain higher radiance precision. The GPC will
send a letter to the whole Working Group soliciting opinions on these issues.Two other questions about
NOAA operations with GOES-I were raised: the new satellite has much more flexibility in selecting imaging
modes, so that rapid scans may interrupt full images routinely. Such interruptions, if lengthy, too numerous
or not carefully controlled may affect the quality of the ISCCP analysis by making the diurnal phase of the
data much more irregular and also making erroneous navigation (which depends on scanline number) more
likely. We will request that NOAA plan to preserve the full images on the synoptic hours and avoid rapid
scan interruptions if at all possible. The onboard IR calibration frequency will be increased significantly from
once every week or two to several times daily; however, the GOES-NEXT format does not attach this
information to a particular image. We will request that NOAA either schedule regular calibrations (eg, just
before synoptic hour images) or collect the entire calibration history for delayed delivery to the GPC (as is
currently done with the navigation information).
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 health of GMS-4, METEOSAT-3 (at 75 W), METEOSAT-4, METEOSAT-5, GOES-7, NOAA-11 and
NOAA-12 remained good. NOAA-I was not recovered. Investigation has not yet identified the cause of the
failure, so the schedule to launch NOAA-J has not been accelerated.
Stage B3: July 83 - June 91Stage CD: July 83 - December 91Stage C1: July 83 - June 91Stage C2: July
83 - June 91
Delivering sea ice correlative data for 92 to the GPC.
Delivery backlog for B3 data = 21 months (with respect to planned schedule). B3 data for 96 months have
been archived.
Delivery backlog for C1/C2 data = 21 months (with respect to planned schedule). C1 data for 96 months
have been archived.