A New Fall-Rate Equation for T-5 Expendable Bathythermograph (XBT) by TSK

2005 ◽  
Vol 61 (1) ◽  
pp. 115-121 ◽  
Author(s):  
Shoichi Kizu ◽  
Hiroyuki Yoritaka ◽  
Kimio Hanawa
Keyword(s):  
Rate Equation ◽  
Fall Rate ◽  
Expendable Bathythermograph

scholarly journals Comparison of the fall rate and structure of recent T-7 XBT manufactured by Sippican and TSK

Ocean Science ◽  
2011 ◽  
Vol 7 (2) ◽  
pp. 231-244 ◽  
Author(s):  
S. Kizu ◽  
C. Sukigara ◽  
K. Hanawa
Keyword(s):  
Quadratic Form ◽  
Rate Equation ◽  
Total Weight ◽  
Rate Coefficients ◽  
Fall Rate ◽  
Expendable Bathythermograph ◽  
Structural Differences ◽  
Fall Rates ◽  
The Difference ◽  
Temperature Depth

Abstract. The fall rate of recent T-7 expendable bathythermograph (XBT; 760 m) is evaluated based on a series of concurrent measurement with a calibrated Conductivity Temperature Depth profiler (CTD) in the sea east of Japan. An emphasis is placed on comparing the fall rates of T-7 produced by the two present manufacturers, the Lockheed Martin Sippican Inc., and the Tsurumi Seiki Co. Ltd., which have been believed to be identical but had never been compared directly. It is found that the two manufacturers' T-7 fall at rates different by about 3.5%. The Sippican T-7 falls slower than given by the fall-rate equation (FRE) of Hanawa et al. (1995) by about 2.1%, and the TSK T-7 falls faster by about 1.4%. The fall-rate coefficients estimated based on the sea test by applying the equation of traditional quadratic form, d(t)=at−bt2 where d is depth in meters and t is the time elapsed, in seconds, are a=6.553 (m s−1) and b=0.00221 (m s−2) for the LMS T-7, and a=6.803 (m s−1) and b=0.00242 (m s−2) for the TSK T-7. By detail examination of the probes, we found that the two companies' T-7 have different total weight and many structural differences. Because the difference in the fall rate is about twice larger than the difference in weight (about 2%), it is inferred that the structural differences give sizable impact to the difference in their fall rates. Our results clearly show that the recent T-7 of the two companies needs to be discriminated.

scholarly journals Comparison of the fall rate and structure of recent T-7 XBT manufactured by Sippican and TSK

2010 ◽  
Vol 7 (5) ◽  
pp. 1811-1847 ◽  
Author(s):  
S. Kizu ◽  
C. Sukigara ◽  
K. Hanawa
Keyword(s):  
Quadratic Form ◽  
Water Entry ◽  
Rate Coefficients ◽  
Fall Rate ◽  
Current Standard ◽  
Expendable Bathythermograph ◽  
Structural Differences ◽  
Fall Rates ◽  
The Difference ◽  
Temperature Depth

Abstract. The fall rate of recent T-7 expendable bathythermograph (XBT) is evaluated based on a series of concurrent measurement with a calibrated Conductivity Temperature Depth profiler (CTD) in the sea east of Japan. An emphasis is placed on comparing the fall rates of T-7 produced by the two present manufacturers, the Lockheed Martin Sippican Inc., and the Tsurumi Seiki Co. Ltd., which have been believed to be identical but had never been compared directly. It is found that the two manufacturers' T-7 fall at rates different by about 3.5%. The Sippican T-7 falls slower than the current standard equation by Hanawa et al. (1995) gives by about 2.1%, and the TSK T-7 falls faster than it tells by about 1.4%. The fall-rate coefficients estimated based on the present sea test by applying the equation of traditional quadratic form, d(t)=at−bt2 where d is depth in meters and t is the time elapsed, since the water entry of the probe, in seconds, are a=6.553 and b=0.00221 for the LMS T-7, and a=6.803 and b=0.00242 for the TSK T-7. By detail examination of the probes, it is revealed that the two companies' T-7 have different total weight and many structural differences. Because the difference in the fall rate is about twice larger than the difference in weight (about 2%), it is inferred that those structural differences give sizable impact to the difference in their fall rates. Our results clearly show that the recent T-7 of the two companies needs to be discriminated.

scholarly journals Identifying and Estimating Biases between XBT and Argo Observations Using Satellite Altimetry

2010 ◽  
Vol 27 (1) ◽  
pp. 226-240 ◽  
Author(s):  
Pedro N. DiNezio ◽  
Gustavo J. Goni
Keyword(s):  
Rate Equation ◽  
Satellite Altimetry ◽  
Terminal Velocity ◽  
Height Anomaly ◽  
Fall Rate ◽  
Argo Data ◽  
Least Squares Adjustment ◽  
Systematic Biases ◽  
In Situ Observations

Abstract A methodology is developed to identify and estimate systematic biases between expendable bathythermograph (XBT) and Argo observations using satellite altimetry. Pseudoclimatological fields of isotherm depth are computed by least squares adjustment of in situ XBT and Argo data to altimetry-derived sea height anomaly (SHA) data. In regions where the correlations between isotherm depth and SHA are high, this method reduces sampling biases in the in situ observations by taking advantage of the high temporal and spatial resolution of satellite observations. Temperature profiles from deep XBTs corrected for a bias identified and adopted during the 1990s are considered in this study. The analysis shows that the pseudoclimatological isotherm depths derived from these corrected XBTs are predominantly deeper than the Argo-derived estimates during the 2000–07 period. The XBT-minus-Argo differences increase with depth consistent with hypothesized problems in the XBT fall-rate equation. The depth-dependent XBT-minus-Argo differences suggest a global positive bias of 3% of the XBT depths. The fact that this 3% error is robust among the different ocean basins provides evidence for changes in the instrumentation, such as changes in the terminal velocity of the XBTs. The value of this error is about the inverse of the correction to the XBT fall-rate equation (FRE) implemented in 1995, suggesting that this correction, while adequate during the 1990s, is no longer appropriate and could be the source of the 3% error. This result suggests that for 2000–07, the XBT dataset can be brought to consistency with Argo by using the original FRE coefficients without the 1995 correction.

scholarly journals An Assessment of the XBT Fall-Rate Equation in the Southern Ocean

2018 ◽  
Vol 35 (4) ◽  
pp. 911-926 ◽  
Author(s):  
Natalia Ribeiro ◽  
Mauricio M. Mata ◽  
José Luiz L. de Azevedo ◽  
Mauro Cirano
Keyword(s):  
Southern Ocean ◽  
Rate Equation ◽  
World Ocean ◽  
Heat Content ◽  
Correction Method ◽  
Spatial And Temporal Variability ◽  
Fall Rate ◽  
Regional Environment ◽  
The World ◽  
Ocean Region

AbstractIn this study a set of 157 collocated XBT (DB/T7 type) and CTD stations distributed across three different regions of the Southern Ocean is explored using the manufacturer’s fall-rate equation (FRE), which is a classic correction method, and new correction methods to investigate how the regional environment characteristics may impact a probe’s descent and the corresponding depth estimates. Regional coefficients were estimated for all three basins and for the Southern Ocean as a whole. The manufacturer’s FRE proved to perform better in high latitudes than in the rest of the World Ocean, overestimating the true depth by only 2%. The overall depth bias was positive, further supporting the hypothesis of a regional dependence of the XBT fall rate on water temperature, which leads to a general overestimation of ocean heat content in the upper layer (~4.79 × 109 J or ~10%). The pure thermal bias was found to be mostly negative, which is likely to be related to temperature errors. However, the Southern Ocean region is notoriously undersampled when compared to the rest of the World Ocean as well, as it is associated with strong spatial and temporal variability, thus raising the overall uncertainty on that estimate. Moreover, although the manufacturer’s FRE has a satisfying performance in the Southern Ocean, the current community’s recommended correction method still leads to improved temperature values in those waters. Finally, more studies are needed in order to fully understand the XBT regional bias and its implications for climate studies in the region.

scholarly journals Early Dynamics of Deep Blue XBT Probes

2015 ◽  
Vol 32 (12) ◽  
pp. 2253-2263 ◽  
Author(s):  
Francis Bringas ◽  
Gustavo Goni
Keyword(s):  
Temperature Profile ◽  
Rate Equation ◽  
Heat Content ◽  
Ocean Heat Content ◽  
Ocean Currents ◽  
Time Dependent ◽  
Global Ocean ◽  
Fall Rate ◽  
Deep Blue ◽  
Height Dependence

AbstractExpendable bathythermographs (XBTs) are probes widely used to monitor global ocean heat content, variability of ocean currents, and meridional heat transports. In the XBT temperature profile, the depth is estimated from the time of descent in the water using a fall-rate equation. There are two main errors in these profiles: temperature and depth errors. The reduction of error in the estimates of the depth allows a corresponding reduction in the errors in the computations in which XBTs are used. Two experiments were carried out to study the effect of the deployment height on the depth estimates of Deep Blue XBT probes. During these experiments, XBTs were deployed from different heights. The motion of the probes after entering the water was analyzed to determine the position and the velocity of the probes as a function of time, which was compared to that obtained using the Hanawa et al. fall-rate equation. Results showed a difference or offset between the experimentally observed depths and those derived from Hanawa et al. This offset was found to be linked to the deployment height. To eliminate the offset in the fall-rate equation for XBTs deployed from different heights, a methodology is proposed here based on the initial velocities of the probes in the water (or deployment height). Results indicate that the depth estimates in the profiles need to be corrected for an offset, which in addition to having a launch height dependence is time dependent during the first 1.5 s of descent of the probe in the water, and constant after that.

scholarly journals Time, Probe Type, and Temperature Variable Bias Corrections to Historical Expendable Bathythermograph Observations

2014 ◽  
Vol 31 (8) ◽  
pp. 1793-1825 ◽  
Author(s):  
Lijing Cheng ◽  
Jiang Zhu ◽  
Rebecca Cowley ◽  
Tim Boyer ◽  
Susan Wijffels
Keyword(s):  
Water Temperature ◽  
World Ocean ◽  
Heat Content ◽  
Terminal Velocity ◽  
Global Scale ◽  
Global Ocean ◽  
Probe Type ◽  
Fall Rate ◽  
Dominant Term ◽  
Expendable Bathythermograph

Abstract Systematic biases in historical expendable bathythermograph (XBT) data are examined using two datasets: 4151 XBT–CTD side-by-side pairs from 1967 to 2011 and 218 653 global-scale XBT–CTD pairs (within one month and 1°) extracted from the World Ocean Database 2009 (WOD09) from 1966 to 2010. Using the side-by-side dataset, it was found that both the pure thermal bias and the XBT fall rate (from which the depth of observation is calculated) increase with water temperature. Correlations between the terminal velocity A and deceleration B terms of the fall-rate equation (FRE) and between A and the offset from the surface terms are obtained, with A as the dominant term in XBT fall-rate behavior. To quantify the time variation of the XBT fall-rate and pure temperature biases, global-scale XBT–CTD pairs are used. Based on the results from the two datasets, a new correction scheme for historical XBT data is proposed for nine independent probe-type groups. The scheme includes corrections for both temperature and depth records, which are all variable with calendar year, water temperature, and probe type. The results confirm those found in previous studies: a slowing in fall rate during the 1970s and 2000s and the large pure thermal biases during 1970–85. The performance of nine different correction schemes is compared. After the proposed corrections are applied to the XBT data in the WOD09 dataset, global ocean heat content from 1967 to 2010 is reestimated.

scholarly journals Biases in Expendable Bathythermograph Data: A New View Based on Historical Side-by-Side Comparisons

2013 ◽  
Vol 30 (6) ◽  
pp. 1195-1225 ◽  
Author(s):  
Rebecca Cowley ◽  
Susan Wijffels ◽  
Lijing Cheng ◽  
Tim Boyer ◽  
Shoichi Kizu
Keyword(s):  
Time History ◽  
Fall Rate ◽  
Ocean Temperature ◽  
Temperature Bias ◽  
Deep Blue ◽  
Bias Model ◽  
Fitting Method ◽  
Expendable Bathythermograph ◽  
History Of ◽  
Temperature Depth

Abstract Because they make up 56% of ocean temperature profile data between 1967 and 2001, quantifying the biases in expendable bathythermograph (XBT) data is fundamental to understanding the evolution of the planetary energy and sea level budgets over recent decades. The nature and time history of these biases remain in dispute and dominate differences in analyses of the history of ocean warming. A database of over 4100 side-by-side deployments of XBTs and conductivity–temperature–depth (CTD) data has been assembled, and this unique resource is used to characterize and separate out the pure temperature bias from depth error in a way that was not previously possible. Two independent methods of bias extraction confirm that the results are robust to bias model and fitting method. It was found that there is a pure temperature bias in Sippican probes of ~0.05°C, independent of depth. The temperature bias has a time dependency, being larger (~0.1°C) in the earlier analog acquisition era and being likely due to changes in recorder type. Large depth errors are found in the 1970s–80s in shallower-measuring Sippican T4/T6 probe types, but the deeper-measuring Sippican T7/Deep Blue (DB) types have no error during this time. The Sippican T7/DB fall rate slows from ~1990 onward. It is found that year-to-year variations in fall rate have a bigger effect on corrections to the global XBT database than do any small effects of ocean temperature on fall rate. This study has large implications for the future development of better schemes to correct the global historical XBT archive.

scholarly journals Turbulent and Transitional Modeling of Drag on Oceanographic Measurement Devices

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
J. P. Abraham ◽  
J. M. Gorman ◽  
F. Reseghetti ◽  
E. M. Sparrow ◽  
W. J. Minkowycz
Keyword(s):  
Global Warming ◽  
Drag Coefficient ◽  
Computational Fluid Dynamic ◽  
Rate Equation ◽  
Fluid Dynamic ◽  
Heat Content ◽  
Fall Rate ◽  
Dynamic Techniques ◽  
Measurement Devices

Computational fluid dynamic techniques have been applied to the determination of drag on oceanographic devices (expendable bathythermographs). Such devices, which are used to monitor changes in ocean heat content, provide information that is dependent on their drag coefficient. Inaccuracies in drag calculations can impact the estimation of ocean heating associated with global warming. Traditionally, ocean-heating information was based on experimental correlations which related the depth of the device to the fall time. The relation of time-depth is provided by a fall-rate equation (FRE). It is known that FRE depths are reasonably accurate for ocean environments that match the experiments from which the correlations were developed. For other situations, use of the FRE may lead to depth errors that preclude XBTs as accurate oceanographic devices. Here, a CFD approach has been taken which provides drag coefficients that are used to predict depths independent of an FRE.

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