Make A Graph

Dataset Title:	Great Lakes Monthly Chlorophyll Concentration Data (2012 - 2023)
Institution:	CoastWatch Great Lakes Node (Dataset ID: GR_monthly_CHL_test)
Information:	Summary \| License \| FGDC \| ISO 19115 \| Metadata \| Background \| Data Access Form \| Files

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Graph Type:
X Axis:
Y Axis:
Color:

Dimensions

Start

Stop

time (UTC)

specify just 1 value →

latitude (degrees_north)

longitude (degrees_east)

Graph Settings
Color Bar:	Continuity:	Scale:
Minimum:	Maximum:	N Sections:
Draw land mask:
Y Axis Minimum:	Maximum:

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

Optional:
Then set the File Type: (File Type information)
and

or view the URL:
(Documentation / Bypass this form

)

Click on the map to specify a new center point.

Zoom:

[The graph you specified. Please be patient.]

Things You Can Do With Your Graphs

Well, you can do anything you want with your graphs, of course. But some things you might not have considered are:

Web page authors can embed a graph of the latest data in a web page using HTML <img> tags.
Anyone can use ERDDAPs Slide Sorter to build a personal web page that displays graphs with the latest data (or other images or HTML content), each in its own, draggable slide.

The Dataset Attribute Structure (.das) for this Dataset

Attributes {
  time {
    String _CoordinateAxisType "Time";
    Float64 actual_range 1.3266288e+9, 1.7026416e+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";
    Float32 actual_range 41.0, 49.0;
    String axis "Y";
    String ioos_category "Location";
    String long_name "Latitude";
    String standard_name "latitude";
    String units "degrees_north";
  }
  longitude {
    String _CoordinateAxisType "Lon";
    Float32 actual_range -92.5, -76.0;
    String axis "X";
    String ioos_category "Location";
    String long_name "Longitude";
    String standard_name "longitude";
    String units "degrees_east";
  }
  chl {
    Float32 _FillValue -9999.0;
    String ioos_category "Ocean Color";
    String long_name "Chlorophyll Concentration";
    String standard_name "concentration_of_chlorophyll_in_great_lakes";
    String units "mg m^-3";
  }
  NC_GLOBAL {
    String _NCProperties "version=2,netcdf=4.8.1,hdf5=1.12.1";
    String cdm_data_type "Grid";
    String comment "The algorithm is developed at NOAA CoastWatch application team. Reprocesed at CoastWatch Great Lakes Node.";
    String Conventions "COARDS, CF-1.10, ACDD-1.3";
    String creator_email "seunghyun.son@noaa.gov";
    String creator_name "SeungHyun Son";
    String creator_url "https://coastwatch.noaa.gov/";
    Float64 Easternmost_Easting -76.0;
    Float64 geospatial_lat_max 49.0;
    Float64 geospatial_lat_min 41.0;
    Float64 geospatial_lat_resolution 0.008988764044943821;
    String geospatial_lat_units "degrees_north";
    Float64 geospatial_lon_max -76.0;
    Float64 geospatial_lon_min -92.5;
    Float64 geospatial_lon_resolution 0.01273148148148148;
    String geospatial_lon_units "degrees_east";
    String grid_mapping_long_name "CRS definition";
    String grid_mapping_name "latitude_longitude";
    String history 
"The original HDF file is developed at NOAA CoastWatch Application team, reprocessed at CoastWatch Great Lakes Node,Created on 2024-12-09T19:00:02.232463
2025-02-05T06:01:06Z (local files)
2025-02-05T06:01:06Z https://apps.glerl.noaa.gov/griddap/GR_monthly_CHL_test.das";
    String infoUrl "https://coastwatch.noaa.gov";
    String institution "CoastWatch Great Lakes Node";
    String keywords "chl, chlorophyll, coastwatch, color, concentration, concentration_of_chlorophyll_in_great_lakes, data, great, great lakes, lakes, month, monthly, noaa, ocean, ocean color, 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.";
    Float64 Northernmost_Northing 49.0;
    String references "https://coastwatch.noaa.gov";
    String source "/data/data658/cw_apt/sat_pub/mapped/viirs_snpp/GREATLAKES/CHL/3FLAGS/DAY/202312/V20231231Txxxx_gl_chls.hdf";
    String sourceUrl "(local files)";
    Float64 Southernmost_Northing 41.0;
    String standard_name_vocabulary "CF Standard Name Table v70";
    String summary "Chlorophyll concentration data from satellite observations (2012 -2023).";
    String time_coverage_end "2023-12-15T12:00:00Z";
    String time_coverage_start "2012-01-15T12:00:00Z";
    String title "Great Lakes Monthly Chlorophyll Concentration Data (2012 - 2023)";
    Float64 Westernmost_Easting -92.5;
  }
}

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.