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You are here: NODC Home > Ocean Climate Laboratory > OCL Products > XBT Bias > Cowley corrections

Application of corrections to original XBT data
based on Cowley, R., S. Wijffels, L. Cheng, T. Boyer, S. Kizu: Biases in Expendable BathyThermograph data: a new view based on historical side-by-side comparisons, accepted by the Journal of Atmospheric and Oceanic Technology.

Step 1: Identify appropriate correction

Corrections are provided for T4/T6 (Sippican), T7/Deep Blue (Sippican), TSK T6 and TSK T7/Deep Blue.

If manufacturer is not given the deploying country and year of deployment and maximum depth should be used to identify probe type.

Deploying country: TSK types are applied to: Japan, Taiwan, Korea, Thailand, China. All other countries are designated Sippican.

Table 1 contains the information on earliest to market and depth cutoffs for each probe type.

Probe Type Earliest date to market
(dd/mm/yyyy)		 Nominal
depth (m)		 Depth
cutoff (m)		 Approximate percentage
in WOD09 (of total XBTs)
Sippican T4 6/14/1965 460 550 49.00%
Sippican T6 4/14/1968 460 550  
Sippican T7 6/20/1967 760 950 29.70%
Sippican Deep Blue 4/20/1981 760 950  
TSK T6 7/1/1972 460 550 12.40%
TSK T7 4/1/1978 760 950 1.10%
TSK Deep Blue 8/1/1997 760950  
Other types (no corrections supplied):
Sippican T5 6/3/1971 1830 2500 0.80%
Sippican Fast Deep 9/25/1991 1000 2500 0.25%
Sippican T10 3/24/1972 200 350 5.50%
TSK T10 1/1/1979 200 350 
TSK T5 8/1/1971 1000 2500 0.07%

Probes designated TSK T4 use TSK T6 (TSK does not make T4s). All Sparton XBTs use Sippican corrections.

In the paper, the following additional corrections were applied to other probe types for the Global Ocean Heat Content (GOHC) calculation:

Where a correction was not available for a particular year, T4/T6 corrections were used for T7/DB probes and vice versa for Sippican types. The equivalent Sippican correction was used for TSK types. Sippican T4/T6 corrections were applied to all T10, T11, and unknown types with terminal depth < 550 m. Sippican T7/DB corrections were applied to Sippican Fast Deeps and unknown types with terminal depth ›= 550 m and < than 1005m. Corrections were not applied to T5s or to probes with depths ›= 1005m. XBT data from 1996 to the present with no depth equation information were not included in the GOHC calculation.

Step 2: Convert to Hanawa (1995) fall rates if required.

Step 3: Apply the corrections:

Cowley thermal gradient (TG) corrections:

Z(corrected) = (Z(Hanawa)*(1 - Depth_error_slope)) - Depth_error_offset
T(corrected) = T(original) - Thermal_bias

Where Z(Hanawa) is obtained by applying the Hanawa correction to the observed depth and T(original) is the observed temperature.

Depth error slope is provided in Table 2 for different probe types for the years 1967-2010.
Depth error offset is provided in Table 3 for different probe types for the years 1967-2010.
Thermal bias is provided in Table 4 for different probe types for the years 1967-2010.


  Last modified:    Wed, 20-Feb-2013 19:27 UTC NODC.Webmaster@noaa.gov
 
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