The SeaBASS sea surface temperature (SST) validation system is designed to provide ground-truth of satellite-borne measurements via comparisons with coincident in situ temperature measurements. Successful match-ups are compiled into one global file per date for each different sensor and made available via a simple web-based search engine.
This article explains how to search for and download results, how to work with validation files, and provides background information describing the steps involved in creating validation match-ups.
Table of Contents
All global match-up results are compiled into daily data files, one file per date, per each different satellite sensor. Obtaining these SST validation files involves a two-step process of searching then downloading. 1) Search for a list of URLs of the files that meet your sensor and date criteria using either the web-browser graphical interface or the API search method. 2) Run a script in order to retrieve and download all of the data files in your list. You can then read through multiple files in order to combine data from multiple measurement dates.
You must select at least one satellite sensor in your search query. Optionally, you may adjust the date ranges when measurements occurred (“measured between”), and/or the date ranges when results files were most recently created or modified (“archived between”). Archived dates are modified whenever new or historical in situ datasets are processed (which adds or modifies existing daily files), or when satellite data are reprocessed.
Web browser search method
API search method
Get-requests may be crafted using the following parameters. One or more "sensor" entries are required:
sensor (MODIS-Aqua, MODIS-Terra, VIIRS-SNPP) startdate (earliest measurement date, using the form YYYY-MM-DD) enddate (latest measurement date, using the form YYYY-MM-DD) startarcdate (earliest archived date, using the form YYYY-MM-DD) endarcdate (latest archived date, using the form YYYY-MM-DD
Depending on your desired output format, issue GET requests to one of the following (csv-text, HTML, or JSON, respectively):
https://seabass.gsfc.nasa.gov/search/sst.txt? https://seabass.gsfc.nasa.gov/search/sst.html? https://seabass.gsfc.nasa.gov/search/sst.json?
wget -i sst_results.csv --nocheck-certificate
File names always follow the pattern:
<YYYYMMDD> is the measurement date
<DOY> is the measurement date expressed as DOY
<sensor> and <platform> are the satellite sensor and platform
<#> is the length of the size of a box of satellite pixels centered on the in situ target (i.e., 5 refers to satellite statistics generated from a 5x5 pixel box)
For example, sstval_20190103_003_VIIRS_SNPP_5pixl.tgz
Metadata headers contain summary information about the data in the file and processing information. More information. General tips for interpreting this information include:
Metadata “/fields” (and corresponding “/units”) are especially important, as they describe the columns of data in the data matrix. Field names in SST validation files are based on standardized SeaBASS field names for in situ values and l2gen parameter names for satellite products, but have been modified with additional prefixes and suffixes. As a side note, always refer to field names to interpret a column of data, and do not assume columns are always in the same order in every file.
A defined “/missing” value (e.g., -999) is used to replace values in the data matrix where data were missing or undefined.
Additional descriptive information can be found stored as comments in the metadata headers. Lines in the header beginning with the “!” character include free-form information, such as descriptions of satellite processing versions, and definitions of special terms used in the file.
A few small exceptions to the normal SeaBASS file format rules were made to adapt the file format for storing these results. Notably, the "units" of insitu_date_time contains a space, i.e., yyyy-mm-dd hh:mm:ss (whitespace is not normally allowed.) Other changes include the addition or subtraction of a few specific metadata headers (e.g., +platform, +instrument; -measurement_depth, -cruise, -documents, -calibration_files, -data_type).
In situ fields
The in situ field names are based on SeaBASS’s standardized list of field names modified by adding “insitu_” as a prefix. However, these files are a slightly modified version of the SeaBASS file format, with several new or repurposed in situ-related fields including:
Table of special in situ field names used for SST
|cruisename||brief indicator of original in situ data provider|
|insitu_cmcsst||Canadian Meteorological Center (CMC) SST product|
|insitu_filename||a reference for tracking data provenance|
|insitu_oiavhrr||Optimum Interpolation Advanced Very High Resolution Radiometer (AVHRR) SST product|
|insitu_quality||0 = no quality control, 1 = passed general, 2 = final highest quality, 9 = bad|
|insitu_sample||RSMAS numerical in situ code describing data source (defined in metadata header comments), e.g., 0 = moored buoy, 1 = drifting buoy, 2 = ship, 3 = MAERI, 4 = filter radiometer, 5 = Argo profiler, 6 = coral reef watch buoy|
|insitu_SN||In situ ID., e.g., buoy ID codes, ship alpha-numeric call signs, MAERI instrument names and number, etc.|
Satellite (l2gen output) fields
The fields in the file corresponding to satellite data or other output from l2gen are structured <prefix>_<l2gen-name>_<suffix> where:
For example, MODIS_Aqua_sst_center_pixel_value or MODIS_Terra_bt_8550_median
Datasets of in situ SST measurements are compiled and analyzed at the University of Miami Rosenstiel School of Marine Science (RSMAS). Measurements come from a variety of sources including moored buoys, drifting buoys, ship cruises, MAERI, filter radiometers, argo profilers, and coral reef watch buoys. Information about the source of individual data records can be determined from the validation file under columns including “insitu_sample” (the numerical RSMAS in situ code), and “insitu_sn” (an in situ ID that corresponds to, for example, a particular buoy or ship).