## About Finding the XBT Probe Type Information

The XBT prob type information is based on the following codes:

- DPC$ -> XBT depth correction status. Codes to describe Depth Correction status
- FRA$ -> Fall rate (correction factor for XBT probes)
- FRE$ -> Code for fall rate equation used. (WMO code 1770)
- PEQ$ -> XBT fall rate equation (WMO code 1770)
- PFR$ -> XBT probe type, fall rate equation and recorder type (WMO code 1770 and 4770)
- PRT$ -> XBT probe type (WMO code 1770)
- XEQ$ -> XBT fall rate equation used (WMO code 1770)

The above codes are stored in the "SURF_CODES structure" of the GTSPP ASCII and netCDF format files. The GTSPP data users need to look for a "SRFC_Code" set to any above codes. The values of each code stored in "SRFC_Parm".

The "DPC$" indicates the status of depth correction and the value of "DPC$" could have one of the following states:

- 01 = Known Probe Type, Needs Correction,
- 02 = Known Probe Type, No need to Correct
- 03 = Unknown Probe Type, Not enough information to know what to do, leave alone,
- 04 = Known XBT Probe Type, Correction was done, and
- 05 = Unknown Probe Type, but a correction was done.

If the code, "PFR$", is present, look at the first 3 characters of the value in " SRFC_Parm" as these encode the probe type and the fall rate equation used. Compare these to WMO code table 1770 to determine which equation was used to calculate depth. For example, the value of the PFR$ code could be 04205 where 042 means a Sippican T-7 probe (table 1770) and 05 means a MK12 recorder (table 4770). Note that 041 is also a Sippican T-7 but with different (older) fall rate equation coefficients. Unless information is specifically present, you should assume the old fall rate equations have been used. XBTs that have used the new fall rate equations always have information about the probe, recorder and the equations.