JPL Atlas of Monthly Mean Global Surface Ocean Variables (1987-1999 satellite data)
D. Halpern et al.
JPL Product #001

Investigators Dr. David Halpern, Principal investigator, JPL
Dr. O. Brown, U of Miami
Dr. D. Dixon, Colorado College
Mr. W. Knauss, JPL
Dr. M. Freilich, Oregon State University
Dr. L. Fu, JPL
Ms. J. Newman, JPL
Mr. G. Pihos, JPL
Dr. F. Wentz, Remote Sensing Systems
Dr. V. Zlotnicki, JPL
Dr. G. Feldman, NASA GSFC
SMP Project None specific to this product.
Product Monthly Mean Global Surface Ocean Variables 1987-1999 (Halpern et al.)
Description IntroductionThese data are part of the Product Number 001 of the Multi-parameter data products made available from the NASA Jet Propulsion Laboratory Physical Oceanography Distributed Active Archive Center (PODAAC)
Source/sensor: ARGOS Buoys, AVHRR/2, ERS-1 and -2, GEOSAT, NSCAT, SSM/I, TOPEX/Poseidon, TMI, SeaWiFS
Coverage: 1987-1999, global
Abstract: The Monthly Mean Global Surface Ocean Variables data set consists of monthly mean averages of global sea surface temperature, sea surface height, significant wave height, chlorophyll-a concentration, surface wind speed, surface wind velocity and near-surface current. These data sets are associated with a series of printed atlases by Halpern et al. (1991, 1992a, 1992b, 1993a, 1993b, 1994, 1995, 1998, 1999, 2000). Please note that the years over which the monthly averages were calculated and the distance between measurements differ for each data set.
The tables below provide information specific to each data set.
Submitted March 2001
Data access Climatology NetCDF files
e-Citation Halpern et al., Live Access to US JGOFS SMP Data: Monthly Mean Global Surface Ocean Variables (D. Halpern et al.). U.S. JGOFS. iPub: Sep 2003. 'date you accessed the data' http://usjgofs.whoi.edu/las/servlets/dataset
References David Halpern, O. Brown, D. Dixon, W. Knauss, M. Freilich, L. Fu, J. Newman, G. Pihos, F. Wentz, V. Zlotnicki, G. Feldman. 2001. Annual atlases of global oceanographic data products for 1987-1999. JPL Product #001.
Documentation http://podaac.jpl.nasa.gov:2031/DATASET_DOCS/halpern_atlas.html
Other References: In addition, an extensive list of printed atlases (almost yearly between 1991 through the present) associated with this product is available at: http://podaac.jpl.nasa.gov/order/order_datacol.html#Product001

Additional notes: IMPORTANT:  these data coincide precisely with data used to develop the year-to-year atlases provided by Dave Halpern and others at JPL.  There is no reprocessing of earlier data sets to incorporate changes in sensors and/or algorithms.  That is, some datasets are not "seamless" in the sense of accounting for changes in sensors/and or algorithms, and investigators who wish to incorporate these data in their analyses should look into other sources which have attempted to create a more accurate time-series of the data.  These data are made available here to add convenience of examining the types of data available, their temporal and spatial coverage, and their applicability to various research projects.

The original data (available via ftp at: ftp://podaac.jpl.nasa.gov/pub/data_collections/monthly_mean_atlas/) are provided in raw binary format. These were converted to NetCDF format for use on the US JGOFS SMP Live Acess Server.  The table below is the one provided on the PODAAC site.  Links within the table provide additional information about the NetCDF files.
Data Set
Temporal Coverage
 Spatial Resolution
ARGOS Buoy Drift 1989 - 1992 Measurements given at location of buoys
AVHRR/2 Sea Surface Temperature 1987 - 1999 Global Grid of 1024 pixels longitude by 512 pixels latitude
ERS-1 AMI Wind Vectors 1992 - May 1996 Global Grid of 1080 pixels longitude by 540 pixels latitude
ERS-2 AMI Wind Vectors June 1996 - 1997 Global Grid of 1080 pixels longitude by 540 pixels latitude
GEOSAT Sea Surface Height 1987 - 1988 Global Grid of 1080 pixels longitude by 540 pixels latitude
NSCAT Wind Vectors Jan 1997 - June 1997 Global Grid of 1080 pixels longitude by 540 pixels latitude
SSM/I Wind Speed 1987 - 1999 Global Grid of 1080 pixels longitude by 540 pixels latitude
TOPEX/Poseidon Sea Surface Height (SSH) and Significant Wave Height (SWH) 1993 - 1999 SSH 1993: Global Grid of 540 pixels longitude by 270 pixels latitude

SSH 1994: Global Grid of 539 pixels longitude by 396 pixels latitude

SSH 1995-1998: Global Grid of 540 pixels longitude by 540 pixels latitude

SWH 1998: Global Grid of 360 pixels longitude by 180 pixels latitude
 
SeaWiFS Chlorophyll-a Concentration  1998-1999 Global Grid of 720 pixels longitude by 360 pixels latitude
TMI Sea Surface Temperature  1998-1999 Global Grid of 1440 pixels longitude by 320 pixels latitude

Additional information is available: http://podaac.jpl.nasa.gov/order/order_datacol.html

These data were converted to NetCDF format by J Kleypas, on Oct 1, 2001.


AVHRR/2 Sea Surface Temperature
1987 - 1999
Halpern et al. description:  Data extends from ~70 N to ~ 70 S. Data at high and low latitudes is limited by ice cover and by cloud cover. In addition, because this data was processed by NESDIS for operational purposes, areas of less interest for operational purposes have less processed data. For this data set, four consecutive 7-day averages (produced by RSMAS) are arithmetically averaged to form 28-day mean MCSST values, (Halpern et al., 1992). "A 1024 x 512 grid was created by computing the arithmetic mean of four 18 km x 18 km MCSSTs adjacent to each other in a two dimensional array. The average MCSSTs of 4-element groups, which were independent of each other, represent an approximate 1/3 degree by 1/3 degree gridded MCSST data set." (This material is taken directly from Halpern et al., 1992)
DATE DIMENSIONS NOTES
1987-1988 SST:
1024 pixels lon X 512 pixels lat X 24 months 
lon limits: 0.1758 (E) to 359.8242 (E) (cell centers) 
lat limits: 89.8242 (S) to 89.8242 (N) (cell centers) 
units: deg Celcius 
missing value = 1.e30 
land mask: none		 Missing data were represented with '-999900' in the original file; in the NetCDF file, this value was replaced with 1.e30.
1989-1994 SST:
1024 pixels lon X 512 pixels lat X 72 months
lon limits: 0.1758 (E) to 359.8242 (E) (cell centers)
lat limits: 89.8242 (S) to 89.8242 (N) (cell centers)
units: deg Celcius
missing value = 1.e30
land mask: 1=land; 0=ocean		 Missing data were represented with '-999900' in the original file; in the NetCDF file, this value was replaced with 1.e30.
1995-1999 SST, OBS:
1024 pixels lon X 512 pixels lat X 60 months
lon limits: 0.1758 (E) to 359.8242 (E) (cell centers)
lat limits: 89.8242 (S) to 89.8242 (N) (cell centers)
units: deg Celcius
missing value = 1.e30
land mask: none		 Missing data were represented with '0.0' in the original file; in the NetCDF file, SST values where no observations were made were replaced with 1.e30.

Note that the data for each month does not entirely correspond to a calender month. The days over which the data was collected are indicated in the atlas.

The 'obs' variable contains the number of data values that were used to compute the mean temperature value at a particular grid point. An 'obs' value equal to 0 (zero) indicates that there were NO temperature values for that grid point (over the ocean -- and obviously not over land). The 'obs' array values greater than zero can therefore be used to identify legitimate values of SST for each grid point.


ERS-1 & ERS-2 AMI Wind Vectors
1992 - 1999
Halpern et al. description:  ERS-1 and ERS-2: The European Space Agency (ESA) European Remote Sensing (ERS-1) satellite orbits at approximately 780 km above sea level. The ERS-1 satellite was designed as a forerunner of a new generation of satellites for environmental monitoring. It is the first civilian satellite since Seasat to carry active microwave instruments. Objectives include: improved understanding of ocean-atmosphere interactions, ocean circulation and energy transfer, Arctic and Antarctic ice sheet mass balance, improved monitoring of dynamic coastal processes and pollution, and improved detection and management of land use changes. The Active Microwave Instrument (AMI) operated at 5.3 GHz (C-band). In the wind scatterometer mode the AMI operated by recording the change in radar reflectivity of the sea due to small ripples (capillary waves) generated by the wind. The AMI has a 500 km groundtrack that is offset 225 km from nadir. The spatial resolution is about 50 km.

ERS-1
DATE DIMENSIONS NOTES
1992-1994 U,V, wind speed, wind direction:
1080 pixels lon X 540 pixels lat X 36 months
lon limits: 0.1667 (E) to 359.8333 (E) (cell centers)
lat limits: 89.8333 (S) to 89.8333 (N) (cell centers)
units: m/s (U,V, wind speed)
units: degrees clockwise from true north (wind direction)
missing value = 1.e30		 The original 1992-1994 ERS-1 data include U,V vectors; but NOT wind speed and direction.Wind speed and direction in the NetCDF file were calculated directly from the U,V vectors.

U,V vectors in original files were reported in cm/s; in NetCDF files, these were converted to m/s.
wind direction:
144 pixels lon X 72 pixels lat X 53 months
lon limits:  1.25 (E) to 358.75 (E) (cell centers)
lat limits: -88.75 (S) to  88.75 (N) (cell centers)
units: degrees clockwise from true north
missing value = 1.e30		 Wind direction data provided here is at lower resolution than that of the original data (1080X540 - see above). These are provided to maintain consistency with the resolution provided by Halpern et al. for other years of ERS wind direction: Halpern et al. computed wind direction "on the basis of a 2.5 by 2.5 lat/lon degree average at each grid point for each month." but provided only a 72 X 36 grid [only every other value was plotted in the ERS plots in Halpern et al. 2001. (JPL Publ. 01-01; see p. 5)].

Wind direction for 1992-1994 data were computed by (1) averaging U and V to a 2.5 deg grid (144 X 72); (2) calculating wind direction from these average U and V vectors.  NOTE however, that the wind direction data presented here provide all values at the 2.5 deg resolution (144 X 72 grid).
1995 - MAY 1996 wind speed:
1080 pixels lon X 540 pixels lat X 17 months
lon limits: 0.1667 (E) to 359.8333 (E) (cell centers)
lat limits: 89.8333 (S) to 89.8333 (N) (cell centers)
units: m/s
missing value = 1.e30		 The 1995 - MAY 1996 ERS-1 data are provided as speed and direction in the original files.  Halpern et al. did not provide U,V vectors in the original data and these were not calculated/included in the NetCDF files.
wind direction:
72 pixels lon X 36 pixels lat X 53 months
lon limits:  1.25 (E) to 356.25 (E) (cell centers)
lat limits: -88.75 (S) to  86.25 (N) (cell centers)
units: degrees clockwise from true north
missing value = 1.e30		 Halpern et al. computed wind direction "on the basis of a 2.5 by 2.5 lat/lon degree average at each grid point for each month."
Although the wind direction data were computed at 2.5 X 2.5 deg resolution, the 72X36 file size reflects that only every other value is provided, as indicated in description of ERS plots in Halpern et al. 2001. (JPL Publ. 01-01; see p. 5).

ERS-2
DATE DIMENSIONS NOTES
JUN 1996 - 1999 wind speed: 
1080 pixels lon X 540 pixels lat X 53 months
lon limits: 0.1667 (E) to 359.8333 (E) (cell centers)
lat limits: 89.8333 (S) to 89.8333 (N) (cell centers)
units: m/s
missing value = 1.e30		 The JUN 1996 - 1999 ERS-2 data are provided as speed and direction.  U,V vectors are not provided in the original data and were not calculated/included in the NetCDF files.
wind direction;
72 pixels lon X 36 pixels lat X 53 months
lon limits:  1.25 (E) to 356.25 (E) (cell centers)
lat limits: -88.75 (S) to  86.25 (N) (cell centers)
units: degrees clockwise from true north
missing value = 1.e30		 Halpern et al. computed wind direction "on the basis of a 2.5 by 2.5 lat/lon degree average at each grid point for each month." 
Although the wind direction data were computed at 2.5 X 2.5 deg resolution, the 72X36 file size reflects that only every other value was reported, as indicated in description of ERS plots in Halpern et al. 2001. (JPL Publ. 01-01; see p. 5).


GEOSAT Sea Surface Height
1987 - 1988
Halpern et al. description: 

Elevation of the sea surface relative to a reference ellipsoid: Data consisting of monthly mean 1/3 degree by 1/3 degree values extends from approximately 75N to 75 S. Along each groundtrack, the corrected sea surface height values, (corrected for sources of error as discussed in Halpern et al. 1992), "were resampled at fixed latitudes at about every 7 km using a cubic spline. No interpolation was made over a data gap larger than 3 s (~21 km)." (This material is taken directly from Halpern et al. 1992)

GEOSAT Sea Surface Heights are provided for the years 1987 and 1988. Geosat operated between 1985 and 1989. It was designed by the U.S. Navy primarily for collecting precise measurements of ocean topography for military use, and was later maneuvered into an orbit that allowed data collection of ocean topography measurements.
DATE DIMENSIONS NOTES
1987-1988 SSH:
1080 pixels lon X 540 pixels lat X 24 months
lon limits: 0.1667 (E) to 359.8333 (E) (cell centers)
lat limits: 89.8333 (S) to 89.8333 (N) (cell centers)
units: centimeters
missing value = 1.e30		 Missing data or land were represented with '-999900' in the original file; in the NetCDF file, this value was replaced with 1.e30.
Several lines of data are missing in the original July 1988 file. These missing data points were filled with the missing value (1.e30).


NSCAT Wind Vectors
Jan 1997 - Jun 1997
Halpern et al. description:  The monthly maps are 1/3 x 1/3 degree maps of wind speed overlaid with wind vectors at 2.5 x 2.5 degree resolution.

Note that these data are available for 6 months only: Jan-Jun 1997.
Also note that wind direction is provided at a much coarser resolution than provided for wind speed.
DATE DIMENSIONS NOTES
JAN 1997 - JUN 1997 Wind Speed
1080 pixels lon X 540 pixels lat X 6 months
lon limits: 0.1667 (E) to 359.8333 (E) (cell centers)
lat limits: 89.8333 (S) to 89.8333 (N) (cell centers)
units: m/s
missing value = none designated		 No special values for missing data or land were designated in the original file. 
Wind Direction
72 pixels lon X 36 pixels lat X 6 months
lon limits: 1.25 (E) to 356.25 (E) (cell centers)
lat limits: 88.75 (S) to 86.25 (N) (cell centers)
units: degrees clockwise from true north
missing value = none designated		 No special values for missing data or land were designated in the original file.

NOTE:  although the wind direction data were computed at 2.5 X 2.5 deg resolution, the 72X36 file size reflects that only every other value was reported, as indicated in description of ERS plots in Halpern et al. 2001. (JPL Publ. 01-01; see p. 5):  "The wind direction data are on a 72 X 36 element grid with the origin at -88.75 South latitude and 1.25° East longitude (i.e., a 5x5° lat/lon grid resolution ranging from -88.75 (S) to 86.25 (N) in latitude & from 1.25 to 356.25 in East longitude). The wind direction data, however, have been computed on the basis of a 2.5x2.5° lat/lon average at each grid point for each month." -- from associated fortran program


SSM/I Wind Speed
1987 - 1999
Halpern et al. description: "The Wentz(1989b) GDR contains wind speed values in nonoverlapping areas of 25 km x 25 km, which are arrayed across the 1394-km SSM/I swath width. Geographical coordinates are provided at the center of each 25-km x 25-km region. SSM/I wind speeds within nonoverlapping 1/3 degree by 1/3 degree squares were arithmetically averaged to form the basic data set for the report. The origin of the global 1/3 degree by 1/3 degree grid is 90 N and 0 longitude. Most of the 1/3 degree by 1/3 degree areas contain at least 50 wind speed values per month, or about 1-2 values per day. Coverage of SSM/I wind speeds over the global ocean is nearly complete every 3 days." (This material is taken directly from Halpern, 1992).

These data products consist of wind speeds calculated over water areas (plus coastal, sea ice, and possible sea ice areas) using the algorithms developed by F. Wentz (Remote Sensing Systems 1989, 1992). In this study SSM/I winds are referenced to a 10 m height. The data were derived from the SSM/I (Special Sensor Microwave/Imager) instrument on the DMSP F-8 (Defense Meteorological Satellite Program) satellite and were produced by the Marshall Space Flight Center.
DATE DIMENSIONS NOTES
AUG 1987 - DEC 1999 wind speed:
1080 pixels lon X 540 pixels lat X 149 months
lon limits: 0.1667 (E) to 359.8333 (E) (cell centers)
lat limits: 89.8333 (S) to 89.8333 (N) (cell centers)
units: m/s
missing value = 1.e30
land mask: 1=land; 0=ocean		 Missing data are represented with 1.e30.
Land is represented with -9999 in the original files; these values were replaced with missing values and a land mask is included.

The number of observations for each grid cell were only provided in the original data for the year 1994, and are not provided in the NetCDF files.


TOPEX/Poseidon Sea Surface Height & Significant Wave Height
1993 - 1999
Halpern et al. description: 

Elevation of the sea surface relative to a reference ellipsoid: Data consisting of monthly mean 2/3 degree by 2/3 degree values extends from approximately 66 N to 66 S. Data from both altimeters was used in this data set, (Halpern, 1995). Along each groundtrack, the values "were resampled a 6km intervals using a cubic spline. No interpolation was made over a data gap larger than 3 s (~20 km)." (This material is taken directly from Halpern, 1995).

Note that the TOPEX/Poseidon Sea Surface Height Data are available for three different periods: 1993, 1994, and 1995-1999; while Significant Wave Height data are available only for the 2-year period 1998-1999.  The different periods remain separate because each was originally reported on different grids.

Sea Surface Height

DATE DIMENSIONS NOTES
1993 SSH:
540 pixels lon X 270 pixels lat X 12 months
lon limits: 0.3333 (E) to 359.6667 (E) (cell centers)
lat limits: -89.3333 (S) to 89.3333 (N)
units: centimeters
land mask: 1=land; 0=ocean;
missing value = 1.e30		 Missing values in the original file were 9999; land values were designated as -9999; in the LAS NetCDF file, these were both converted to 1.e30; and a separate land mask was provided.
1994 SSH:
540 pixels lon X 540 pixels lat X 12 months
lon limits: 0.3333 (E) to 359.6667 (E) (cell centers) 
lat limits: -89.8333 (S) to 89.8333 (N)
units: centimeters
land mask: no land mask was provided
missing value = 1.e30		 The original data for this file was reported as:
539 pixels lon X 396 pixels lat X 12 months
lon limits: 0.3333 (E) to 359.3333 (E) (cell centers)
lat limits: -65.8333 (S) to 65.8333 (N)

Missing values in the original file were 3276.70; in the LAS NetCDF file, these were converted to 1.e30
There was no mask or land value provided with the 1994 data.
1995-1999 SSH:
540 pixels lon X 540 pixels lat X 60 months
lon limits: 0.3333 (E) to 359.6667 (E) (cell centers) 
lat limits: -89.8333 (S) to 89.8333 (N)
units: centimeters
land mask: no land mask was provided
missing value = 1.e30;		 Missing values in the original file were 32767; in the LAS NetCDF file, these were converted to 1.e30

Significant Wave Height

DATE DIMENSIONS NOTES
1998-1999 SWH:
360 pixels lon X 180 pixels lat X 24 months
lon limits: 0.5 (E) to 359.5 (E) (cell centers)
lat limits: -89.5 (S) to 89.5 (N) 
units: meters
missing value = 1.e30		 Missing values in the original file were 32627; in the LAS NetCDF file, these were converted to 1.e30. A missing value indicates that there were NO swh values for that grid point.


SeaWiFS Chlorophyll-a Concentration
1998 - 1999
Halpern et al. description:  Data consists of 0.5 degree monthly mean maps of Chlorophyll-a concentration. These data were derived from the 9 km monthly mean data provided by the SeaWiFS Project.

The SeaWiFS Chlorophyll-a Data are available for the 2-year period 1998-1999. Two variables are available for this data set:

  1. chlorophyll-a concentration, in mg m-3;
  2. identifier for cells which are land or have no data (0) versus those for which data ARE available (1).
DATE DIMENSIONS NOTES
1998-1999 CHL, OBS:
720 pixels lon X 360 pixels lat X 24 months
lon limits: 0.25 (E) to 359.75 (E) (cell centers)
lat limits: -89.25 (S) to 89.75 (N)
units: mg m-3
missing value = 1.e30		 No special values for missing data or land were presented in the original file
The OBS variable shows which grid cells had observations (0=no observations; 1=at least 1 observation)


TMI Sea Surface Temperature
1998 - 1999
Halpern et al. description:  Data are 50 km x 50 km nighttime global SST maps.

These data are obtained from the Tropical Rainfall Measuring Mission (TRMM) spacecraft. The data presented here are from the TRMM microwave imager (TMI). The main advantage of this imager is that it is capable of sensing sea surface temperature through clouds. The main disadvantage is that it's spatial coverage is restricted to 40°S - 40°N TMI Sea Surface Temperature data are available for the 2-year period 1998-1999. Halpern et al. (2001) provide only the 0.25X0.25° nighttime SST data. Two variables are available for this data set:

  1. sea surface temperature in °C;
  2. number of observations per grid cell
DATE DIMENSIONS NOTES
1998-1999 SST, OBS:
1440 pixels lon X 320 pixels lat X 24 months
lon limits: 0.125 (E) to 359.875 (E) (cell centers)
lat limits: -39.875 (S) to 39.875 (N)
units: °C
missing value = 1.e30		 No special values for missing data or land were presented in the original file; however, if there were no observations within a grid cell, a missing value of 1.e30 was assigned to that cell.
The OBS variable shows the number of observations in each grid cell