Data Access Form

Dataset Title:	Chlorophyll-a, Aqua MODIS, NPP, L3SMI, Global, 4km, R2022 SQ, 2003- present (Monthly Composite)
Institution:	NASA/GSFC OBPG (Dataset ID: erdMH1chlamday_R2022SQ)
Information:	Summary \| License \| FGDC \| ISO 19115 \| Metadata \| Background \| Files \| Make a graph

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Dimensions	Size	Spacing
time (Centered Time, UTC)	276	30 days 18h 35m 21s (uneven)

latitude (degrees_north)	4320	-0.04166667 (even)

longitude (degrees_east)	8640	0.04166667 (even)

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

chlor_a (Chlorophyll Concentration, OCI 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 1.0267776e+9, 1.7579808e+9;
    String axis "T";
    String ioos_category "Time";
    String long_name "Centered 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";
    Float32 _FillValue NaN;
    Float32 actual_range -89.97917, 89.97916;
    String axis "Y";
    String ioos_category "Location";
    String long_name "Latitude";
    String standard_name "latitude";
    String units "degrees_north";
    Float32 valid_max 90.0;
    Float32 valid_min -90.0;
  }
  longitude {
    String _CoordinateAxisType "Lon";
    Float32 _FillValue NaN;
    Float32 actual_range -179.9792, 179.9792;
    String axis "X";
    String ioos_category "Location";
    String long_name "Longitude";
    String standard_name "longitude";
    String units "degrees_east";
    Float32 valid_max 180.0;
    Float32 valid_min -180.0;
  }
  chlor_a {
    Float32 _FillValue NaN;
    Float64 colorBarMaximum 30.0;
    Float64 colorBarMinimum 0.03;
    String colorBarScale "Log";
    String ioos_category "Ocean Color";
    String long_name "Chlorophyll Concentration, OCI Algorithm";
    String references "Hu, C., Lee Z., and Franz, B.A. (2012). Chlorophyll-a algorithms for oligotrophic oceans: A novel approach based on three-band reflectance difference, J. Geophys. Res., 117, C01011, doi:10.1029/2011JC007395.";
    String standard_name "mass_concentration_of_chlorophyll_in_sea_water";
    String units "mg m-3";
    Float32 valid_max 100.0;
    Float32 valid_min 0.001;
  }
  NC_GLOBAL {
    String _lastModified "2025-11-12T21:05:23.000Z";
    String cdm_data_type "Grid";
    String Conventions "CF-1.6 ACDD-1.3, COARDS";
    String creator_email "data@oceancolor.gsfc.nasa.gov";
    String creator_name "NASA/GSFC/OBPG";
    String creator_type "group";
    String creator_url "https://oceandata.sci.gsfc.nasa.gov";
    String date_created "2025-11-12T21:05:23.000Z";
    Float64 Easternmost_Easting 179.9792;
    Float64 geospatial_lat_max 89.97916;
    Float64 geospatial_lat_min -89.97917;
    Float64 geospatial_lat_resolution 0.04166666589488307;
    String geospatial_lat_units "degrees_north";
    Float64 geospatial_lon_max 179.9792;
    Float64 geospatial_lon_min -179.9792;
    Float64 geospatial_lon_resolution 0.041666674383609215;
    String geospatial_lon_units "degrees_east";
    String history 
"Files downloaded daily from https://oceandata.sci.gsfc.nasa.gov/directdataaccess/Level-3%20Mapped/Aqua-MODIS to NOAA SWFSC ERD (erd.data@noaa.gov)
ERDDAP adds the time dimension
2025-11-19T04:49:15Z (local files)
2025-11-19T04:49:15Z https://coastwatch.pfeg.noaa.gov/erddap/griddap/erdMH1chlamday_R2022SQ.das";
    String id "R2022.0.2/L3/AQUA_MODIS.20250901_20250930.L3b.MO.CHL.nc";
    String identifier_product_doi "10.5067/AQUA/MODIS/L3M/CHL/2022";
    String identifier_product_doi_authority "https://dx.doi.org";
    String infoUrl "https://oceandata.sci.gsfc.nasa.gov";
    String institution "NASA/GSFC OBPG";
    String instrument "MODIS";
    String keywords "algorithm, aqua, biology, center, chemistry, chlor_a, chlorophyll, chlorophyllr, color, concentration, data, earth, Earth Science > Oceans > Ocean Chemistry > Chlorophyll, Earth Science > Oceans > Ocean Chemistry > Chlorophyllr, Earth Science > Oceans > Ocean Chemistry > Pigments > Chlorophyll, flight, goddard, group, gsfc, image, imaging, L3, level, level-3, mapped, mass, mass_concentration_of_chlorophyll_in_sea_water, moderate, modis, modisa, nasa, obpg, ocean, ocean color, oceans, oci, pigments, processing, resolution, science, sea, seawater, smi, space, spectroradiometer, standard, water";
    String keywords_vocabulary "GCMD Science Keywords";
    String l2_flag_names "ATMFAIL,LAND,HILT,HISATZEN,STRAYLIGHT,CLDICE,COCCOLITH,LOWLW,CHLWARN,CHLFAIL,NAVWARN,MAXAERITER,ATMWARN,HISOLZEN,NAVFAIL,FILTER,HIGLINT";
    String license "https://science.nasa.gov/earth-science/earth-science-data/data-information-policy/";
    String map_projection "Equidistant Cylindrical";
    String measure "Mean";
    String naming_authority "gov.nasa.gsfc.sci.oceandata";
    Float64 Northernmost_Northing 89.97916;
    String platform "Aqua";
    String processing_level "L3 Mapped";
    String processing_version "R2022.0.2";
    String product_name "AQUA_MODIS.20250901_20250930.L3m.MO.CHL.chlor_a.4km.nc";
    String project "Ocean Biology Processing Group (NASA/GSFC/OBPG)";
    String publisher_email "erd.data@noaa.gov";
    String publisher_name "NOAA NMFS SWFSC ERD";
    String publisher_type "institution";
    String publisher_url "https://www.pfeg.noaa.gov";
    String source "satellite observations from MODIS-Aqua";
    String sourceUrl "(local files)";
    Float64 Southernmost_Northing -89.97917;
    String spatialResolution "4.638312 km";
    String standard_name_vocabulary "CF Standard Name Table v36";
    String summary "Moderate Resolution Imaging Spectroradiometer on Aqua (MODISA) Level-3 Standard Mapped Image";
    String temporal_range "month";
    String time_coverage_end "2025-09-16T00:00:00Z";
    String time_coverage_start "2002-07-16T00:00:00Z";
    String title "Chlorophyll-a, Aqua MODIS, NPP, L3SMI, Global, 4km, R2022 SQ, 2003-present (Monthly Composite)";
    Float64 Westernmost_Easting -179.9792;
  }
}

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.