[[,amsr-method: Extract Something From an amsr Object

Description

Extract something from the metadata or data slot of an amsr-class object.

The [[ method works for all oce objects, i.e. objects inheriting from oce-class. The purpose, as with the related replacement method, [[<-, is to insulate users from the internal details of oce objects, by looking for items within the various storage slots of the object. Items not actually stored can also be extracted, including derived data, units of measurement, and data-quality flags.

The method uses a two-step process to try to find the requested information. First, a class-specific function is used to try to access the requested information (see “Details of the specialized ... method”). Second, if no match is found, a general function is used (see ‘Details of the general method’). If neither method can locates the requested item, NULL is returned.

Usage

"[["(x, i, j, ...)

Arguments

An amsr object, i.e. one inheriting from amsr-class.

Character string indicating the name of item to extract.

Optional additional information on the i item.

...

Optional additional information (ignored).

Value

In all cases, the returned value is a matrix with with dimension 1440 by 720, with NA values if the satellite data are over land (coded to 0x255), have no observations (coded to 0xfe), are bad observations (coded to 0xfd), indicate sea ice (coded to 0xfc), are are faulty owing to high rain (coded to 0xfb).

Details of the general method

If the specialized method produces no matches, the following generalized method is applied. As with the specialized method, the procedure hinges first on the value of i. First, a check is made as to whether i names one of the standard oce slots, and returns the slot contents if so. Thus, x[["metadata"]] will retrieve the metadata slot, while x[["data"]] and x[["processingLog"]] return those slots. Next, if i is a string ending in the "Unit", then the characters preceding that string are taken to be the name of an item in the data object, and a list containing the unit is returned. This list consists of an item named unit, which is an expression, and an item named scale, which is a string describing the measurement scale. If the string ends in " unit", e.g. x[["temperature unit"]], then just the expression is returned, and if it ends in " scale", then just the scale is returned. Next, if i is a string ending in "Flag", then the corresponding data-quality flag is returned (or NULL if there is no such flag). For example, x[["salinityFlag"]] returns a vector of salinity flags if x is a ctd object. If none of the preceding conditions are met, a check is done to see if the metadata slot contains an item with the provided name, and that is returned, if so. A direct match is required for this condition. Finally, the data slot is checked to see if it contains an item with the name indicated by i. In this case, a partial match will work; this is accomplished by using pmatch. If none of the above-listed conditions holds, then NULL is returned.

Details

Partial matches for i are permitted for metadata, and j is ignored.

Data within the data slot must be matched exactly by name, and may be retrieved with units (the default) or as raw bytes (if j="raw".) The available items are: seconds from the start of day (time), temperature in degC (SST); wind speed in m/s (LFwind and MFwindDay); water vapor content (vaporDay); cloudiness (cloud), and rainfall in mm/h (rain). Each of these is an average across day-time and night-time passes; to get the day/night data separately, use e.g. SSTDay SSTNight, and similarly-named versions of all bands.