Data Access Form

Dataset Title:	Chlorophyll, NOAA NOAA-20 VIIRS, Near Real-Time, Global 4km, Level 3, 2017- present, Daily
Institution:	NOAA NESDIS CoastWatch (Dataset ID: nesdisVHNnoaa20chlaDaily)
Information:	Summary \| License \| FGDC \| ISO 19115 \| Metadata \| Background \| Files \| Make a graph

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Dimensions	Size	Spacing
time (UTC)	1164	1 day 0h 58m 12s (uneven)

altitude (m)	1	(just one value)

latitude (degrees_north)	4788	-0.0375 (even)

longitude (degrees_east)	9602	0.0375 (even)

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

chlor_a (Chlorophyll Concentration, OC3 Algorithm, mg m^-3)

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 1.6299792e+9, 1.7345232e+9;
    String axis "T";
    String bounds "baseline_bounds";
    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";
  }
  altitude {
    String _CoordinateAxisType "Height";
    String _CoordinateZisPositive "up";
    Float64 actual_range 0.0, 0.0;
    String axis "Z";
    String ioos_category "Location";
    String long_name "Altitude";
    String positive "up";
    String standard_name "altitude";
    String units "m";
  }
  latitude {
    String _CoordinateAxisType "Lat";
    Float64 actual_range -89.75625000000002, 89.75625000000001;
    String axis "Y";
    String ioos_category "Location";
    String long_name "Latitude";
    String standard_name "latitude";
    String units "degrees_north";
  }
  longitude {
    String _CoordinateAxisType "Lon";
    Float64 actual_range -180.01875, 180.01874999999998;
    String axis "X";
    String ioos_category "Location";
    String long_name "Longitude";
    String standard_name "longitude";
    String units "degrees_east";
  }
  chlor_a {
    Float32 _FillValue NaN;
    String C_format "%.4g";
    Float64 colorBarMaximum 30.0;
    Float64 colorBarMinimum 0.03;
    String colorBarScale "Log";
    String grid_mapping "coord_ref";
    String ioos_category "Ocean Color";
    String long_name "Chlorophyll Concentration, OC3 Algorithm";
    Float32 missing_value NaN;
    String references "O and #39;Reilly J. E. et al. (1998), Ocean color chlorophyll algorithms for SeaWiFS, J. Geophys. Res., 103(C11), 2493724953";
    String standard_name "mass_concentration_of_chlorophyll_in_sea_water";
    String units "mg m^-3";
    Float32 valid_max 1000.0;
    Float32 valid_min 0.001;
  }
  NC_GLOBAL {
    String cdm_data_type "Grid";
    String Conventions "CF-1.6, COARDS, ACDD-1.3";
    String creator_email "coastwatch.info@noaa.gov";
    String creator_name "NOAA/NESDIS/STAR";
    String creator_url "https://coastwatch.noaa.gov";
    String date_created "2024-12-20T06:16:52Z";
    Float64 Easternmost_Easting 180.01874999999998;
    Float64 geospatial_lat_max 89.75625000000001;
    Float64 geospatial_lat_min -89.75625000000002;
    Float64 geospatial_lat_resolution 0.03750000000000001;
    String geospatial_lat_units "degrees_north";
    Float64 geospatial_lon_max 180.01874999999998;
    Float64 geospatial_lon_min -180.01875;
    Float64 geospatial_lon_resolution 0.037500000000000006;
    String geospatial_lon_units "degrees_east";
    Float64 geospatial_vertical_max 0.0;
    Float64 geospatial_vertical_min 0.0;
    String geospatial_vertical_positive "up";
    String geospatial_vertical_units "m";
    String history 
"2024-12-22T01:57:06Z (local files)
2024-12-22T01:57:06Z https://coastwatch.pfeg.noaa.gov/erddap/griddap/nesdisVHNnoaa20chlaDaily.das";
    String identifier_product_doi_authority "https://dx.doi.org";
    String infoUrl "https://coastwatch.noaa.gov/cw/satellite-data-products/ocean-color/near-real-time/viirs-snpp.html";
    String institution "NOAA NESDIS CoastWatch";
    String instrument "VIIRS";
    String keywords "algorithm, altitude, chemistry, chlor_a, chlorophyll, color, concentration, data, default, Earth Science  > Oceans  > Ocean Chemistry  > Chlorophyll, imager, imager/radiometer, imaging, infrared, L3, level, level-3, mass, mass_concentration_of_chlorophyll_a_in_sea_water, n20, national, NOAA-20, ocean, ocean color, oceans, Oceans  > Ocean Optics  > Ocean Color, optics, orbiting, partnership, polar, polar-orbiting, radiometer, sea, seawater, star, suite, suite/N20, time, VIIRS, viirs, viirs-n, visible, water, ww00";
    String keywords_vocabulary "GCMD Science Keywords";
    String license 
"https://science.nasa.gov/earth-science/earth-science-data/data-information-policy/
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 naming_authority "gov.noaa.coastwatch";
    Float64 Northernmost_Northing 89.75625000000001;
    String OBSERVED_PROPERTY "chlor_a";
    String platform "NOAA-20";
    String processing_level "L2";
    String project "Ocean Color Science Team (NOAA/NESDIS/STAR/OCST)";
    String publisher_email "coastwatch.info@noaa.gov; ncei.info@noaa.gov";
    String publisher_name "NOAA CoastWatch; National Centers for Environmental Information (NCEI)";
    String publisher_url "https://coastwatch.noaa.gov; https://www.ncei.noaa.gov/";
    String source "NOAA-20_VIIRS_chlora";
    String sourceUrl "(local files)";
    Float64 Southernmost_Northing -89.75625000000002;
    String standard_name_vocabulary "CF Standard Name Table v29";
    String summary "Visible and Infrared Imager/Radiometer Suite/Suomi-NPP (VIIRS) Level-3 (WW00), Near Real-Time, Chlorophyll, Global, Daily, processed by NOAA. EXPERIMENTAL.";
    String testOutOfDate "now-2days";
    String time_coverage_end "2024-12-18T12:00:00Z";
    String time_coverage_start "2021-08-26T12:00:00Z";
    String title "Chlorophyll, NOAA NOAA-20 VIIRS, Near Real-Time, Global 4km, Level 3, 2017-present,  Daily";
    Float64 Westernmost_Easting -180.01875;
  }
}

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.