Two types of grids are included, whose difference is clarified later:

• 0.5-degree, 5-day binned (version WOCE-PODAAC-05d-v3.0)
• 1.0-degree, 5-day interpolated (version WOCE-PODAAC-10d-v3.0)

Briefly, the Pathfinder algorithm differs from the MCSST algorithm used since 1981 to process AVHRR in that it includes a number of additional instrument corrections, recovers about twice as many SST values in the presence of clouds as the original MCSST, and uses a 5 month moving window to estimate the coefficients for the central month (the coefficients are used to linearly combine the radiances at the 5 AVHRR frequencies into an SST estimate). It also differs from the widely-used Reynolds SST grids which use as input the MCSST calculation and then combine them with in-situ data using a mapping algorithm to estimate weekly, 1 degree grids (see Reynolds SST; the Reynolds data can be obtained by ftp).

T(,,t) = _i [T(_i, _i,t_i) * exp(-0.6931 * (( - _i)²/ w² + ( - _i)²/ w² + (t - t_i)²/w_t²))]

where w = 1 deg, w = 1 deg, w_t = 2 days

The is performed over all points i inside the volume

| - _i | <= 2.5 deg, | - _i | <= 2.5 deg, | t - t_i | <= 5 days

The first pentad is "centered" on January 3, 1990. The specific dates, summary statistics on each grid, and browse images of each, can be found in the Table of AVHRR Grids with Summary Statistics. A Java program to animate a time series of images between any two dates is also available.

For historical reasons, the output of the interpolation program is scaled to one byte integers. Therefore, the smallest temperature difference that can be seen from these grids is 0.15 .

These plots illustrate the change in data processing for 1990,1993-1999 versus 1991-1992 versus 2000-2001: the 1991-92 data, dubbed version 4.0, were found to have inadequate flagging code; the problem was corrected during January 1998, and reprocessing started with data year 1994. Unfortunately, at the time this DVD folder was generated, the 1991-1992 had not yet been reprocessed with the new flags. A postscript version of this figure is also available.
The figures corresponding to the 1.0-degree interpolated grids are significantly different from the binned-grid statistics. The standard deviations are higher because the data gaps are due to clouds which obscure the same regions of the ocean much of the time, systematically in certain higher and lower energy regions of the ocean. The mean temperature values are lower because a greater number of interpolated lower temperatures (higher latitudes) are included. A postscript version of this figure is also available.

0.5 Degree 9-Year Mean

1.0 Degree Gaussian Interpolated 9-Year Mean

All data files contain the following variables:

• woce_date
  The woce_date represents the center day of the averaging period, in the format YYYYMMDD.

• woce_time
  The woce_time is the nominal center time of the of the averaging period. The units are in Universal Time Coordinate, using the time convention HHMMSS.DD.

• time
  The time represents the Julian day equivalent of the woce_date, set to 0 for 1990-01-01.

• latitude
  The units are in positive degrees for north latitude, negative degrees for south latitude. The format consists of a 4-byte signed real array of dimension 360. The grid nodes are centered on -89.75, -89.25, etc.

• longitude
  The units are in positive degrees. The format consists of a 4-byte signed real array of dimension 720. The grid nodes are centered on 0.25, 0.75, etc.

• depth
  The units are in meters. This value is set to zero.

• sea_surface_temperature
  Sea surface temperatures are in degrees C after the scale_factor and add_offset attribute values are applied. The format consists of a 2-byte SIGNED INTEGER array of dimension 720 x 360 (0.5 degree grids) and 360 x 180 (1.0 degree grids). The value 32767 indicates missing data; the value 32766 indicates land.

• bin_count
  (This variable only exists for the 0.5 degree grids)
  The bin_count contains the number of data points per bin. The format consists of a 1-byte array of dimension 720 x 360. The value 0 indicates land or missing data.

See the SST 0.5° Variables and Attributes and SST 1.0° Variables and Attributes for more detail.

The filenames for the NetCDF files are of the form sst05d19900103.nc or sst10d19900103.nc, depending on whether they are 0.5-deg binned, or 1.0-deg interpolated; this is a WOCE Data Products Committee agreement. However, the filenames for the corresponding GIF files are sst05d0002.gif or sst10d0002.gif, where the date is given in cumulative days, with day 0000=1990-01-01, because the data animation software expects monotonically increasing numbers in the filename. The correspondence between both conventions is in the Table of SST statistics (0.5-deg) or the Table of SST statistics (1.0-deg)

gunzip will decompress files created by gzip. On Windows 95, 98, 2000 or NT use Winzip or pkzip to decompress .gz files. On Mac systems Stuffit will decompress .gz files. For more information on gzip, please refer to the gzip home page at http://www.gzip.org