A MARS request is the way to specify an action on a set of fields or observations. The directives specified in a MARS request have the following syntax:
verb, keyword1 = value 1, ... = ..., keywordN = value N
Where:
| verb: | identifies the action to be taken, e.g. retrieve or list. |
|---|---|
| keyword: | is a known MARS variable, e.g. type or date |
| value: | is the value assigned to the keyword, e.g. Analysis or temperature. |
Keywords may be assigned a single value, a list of values or a range of values.
A list is indicated by the separator /
A range is indicated by using the keywords to as well as / and by.
Examples of different formats for values are given in the table below.
| Format | Example |
|---|---|
| single value | param = temperature/SSRD |
| list of values | step = 12/24/48 |
| range of values | date = 19990104/to/19990110/by/2 |
The following example shows a retrieve request with a mix of single, list and range of values:
retrieve, class = od, stream = oper, expver = 1, date = -1, type = analysis, levtype = model levels, levelist = 1/to/91, param = temperature, grid = 0.1/0.1
Retrieve requests have to specify, at least, directives to identify the data. The ones to identify fields are defined in the MARS Catalogue. Data manipulation (post-processing, such as grid) directives are optional, depending on user needs.