Data Access Form

Dataset Title:	Unbiased Relative Difference of Net Primary Productivity, VIIRS NOAA20 vs MODIS Aqua, 9Km, Monthly, 2018-2022, Global
Institution:	NOAA/NESDIS/CoastWatch/WestCoast (Dataset ID: netpp_psi_noaa20_modis)
Information:	Summary \| License \| FGDC \| ISO 19115 \| Metadata \| Background \| Files \| Make a graph

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Dimensions	Size	Spacing
time (UTC)	60	30 days 10h 10m 10s (uneven)

latitude (degrees_north)	2160	-0.08333334 (uneven)

longitude (degrees_east)	4320	0.08333332 (uneven)

Grid Variables (which always also download all of the dimension variables)

psi (Summation for Calculating Psi, 1)

File type: (more information)

(Documentation / Bypass this form)

(Please be patient. It may take a while to get the data.)

The Dataset Attribute Structure (.das) for this Dataset

Attributes {
  time {
    String _CoordinateAxisType "Time";
    Float64 actual_range 1.5160608e+9, 1.6711488e+9;
    String axis "T";
    String calendar "gregorian";
    String ioos_category "Time";
    String long_name "Time";
    String standard_name "time";
    String time_origin "01-JAN-1970 00:00:00";
    String units "seconds since 1970-01-01T00:00:00Z";
  }
  latitude {
    String _CoordinateAxisType "Lat";
    Float64 actual_range -89.95834, 89.95834;
    String axis "Y";
    String ioos_category "Location";
    String long_name "Latitude";
    String standard_name "latitude";
    String units "degrees_north";
    Float64 valid_max 90.0;
    Float64 valid_min -90.0;
  }
  longitude {
    String _CoordinateAxisType "Lon";
    Float64 actual_range -179.9583, 179.9583;
    String axis "X";
    String ioos_category "Location";
    String long_name "Longitude";
    String source_name "cols";
    String standard_name "longitude";
    String units "degrees_east";
  }
  psi {
    String colorBarContinuous "false";
    String colorBarMaximum "0.4";
    String colorBarMinimum "-0.4";
    Int32 colorBarNSections 8;
    String ioos_category "Other";
    String long_name "Summation for Calculating Psi";
    Float32 missing_value -999.0;
    String units "1";
  }
  NC_GLOBAL {
    String cdm_data_type "Grid";
    String Conventions "COARDS, CF-1.6, ACDD-1.3";
    Float64 Easternmost_Easting 179.9583;
    Float64 geospatial_lat_max 89.95834;
    Float64 geospatial_lat_min -89.95834;
    String geospatial_lat_units "degrees_north";
    Float64 geospatial_lon_max 179.9583;
    Float64 geospatial_lon_min -179.9583;
    String geospatial_lon_units "degrees_east";
    String history 
"2025-05-01T11:35:13Z (local files)
2025-05-01T11:35:13Z https://coastwatch.pfeg.noaa.gov/wcn/erddap/griddap/netpp_psi_noaa20_modis.das";
    String infoUrl "https://coastwatch.pfeg.noaa.gov/projects/netpp";
    String institution "NOAA/NESDIS/CoastWatch/WestCoast";
    String keywords "calculating, data, latitude, longitude, psi, summation, time";
    String license 
"The data may be used and redistributed for free but is not intended
for legal use, since it may contain inaccuracies. Neither the data
Contributor, ERD, NOAA, nor the United States Government, nor any
of their employees or contractors, makes any warranty, express or
implied, including warranties of merchantability and fitness for a
particular purpose, or assumes any legal liability for the accuracy,
completeness, or usefulness, of this information.";
    String map_projection "geographic";
    String NCO "netCDF Operators version 4.9.5 (Homepage = http://nco.sf.net, Code = https://github.com/nco/nco)";
    Float64 Northernmost_Northing 89.95834;
    String proj4_string "+proj=eqc +lat_ts=0 +lat_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs +lon_0=0.000000";
    String project "NOAA CoastWatch Interim Primary Productivity";
    String sourceUrl "(local files)";
    Float64 Southernmost_Northing -89.95834;
    String spatialResolution "9.28 km";
    String standard_name_vocabulary "CF Standard Name Table v70";
    String summary "The unbiased relative difference (Psi) between primary productivity (netPP) calculated using VIIRS NOAA-20 data and MODIS Aqua data. For each pixel, psi is calculated as netPP(viirs)- netPP(modis) divided by the mean of netPP(viirs) and netPP(modis) as described by Mélina et al. 2017. Primary productivity was calculated as described by Behrenfeld and Falkowski 1997. The data are a 5-year mean from Jan 2018 to Dec 2022 and at 9km resolution. Input data for primary productivity were obtained from NASA and included chlorophyll_a, sea surface temperature, and photosynthetically active radiation from either MODIS Aqua or VIIRS NOAA20..";
    String time_coverage_end "2022-12-16T00:00:00Z";
    String time_coverage_resolution "PDM";
    String time_coverage_start "2018-01-16T00:00:00Z";
    String title 
"Unbiased Relative Difference of Net Primary Productivity, VIIRS NOAA20 vs MODIS Aqua, 9Km,
Monthly, 2018-2022, Global";
    Float64 Westernmost_Easting -179.9583;
  }
}

Using griddap to Request Data and Graphs from Gridded Datasets

griddap lets you request a data subset, graph, or map from a gridded dataset (for example, sea surface temperature data from a satellite), via a specially formed URL. griddap uses the OPeNDAP (external link)

Data Access Protocol (DAP) (external link)

and its projection constraints (external link)

The URL specifies what you want: the dataset, a description of the graph or the subset of the data, and the file type for the response.

(easy) You can get data by using the dataset's Data Access Form. It makes the URL for you.
(easy) You can make a graph or map by using the dataset's Make A Graph form. It makes the URL for you.
(not hard) You can bypass the forms and get the data or make a graph or map by generating the URL by hand or with a computer program or script.

griddap request URLs must be in the form
https://coastwatch.pfeg.noaa.gov/erddap/griddap/datasetID.fileType{?query}
For example,
https://coastwatch.pfeg.noaa.gov/erddap/griddap/jplMURSST41.htmlTable?analysed_sst[(2002-06-01T09:00:00Z)][(-89.99):1000:(89.99)][(-179.99):1000:(180.0)]
Thus, the query is often a data variable name (e.g., analysed_sst), followed by [(start):stride:(stop)] (or a shorter variation of that) for each of the variable's dimensions (for example, [time][latitude][longitude]).

For details, see the griddap Documentation.