Robert S. Linzell

The Temperature and Depth Accuracy of Sippican T-5 XBTs

Abstract Thirty-four near-simultaneous pairs of CTD and Sippican model T-5 XBT profiles were obtained during an experiment in the Sargasso Sea during the summer of 1991. The data were analyzed to assess the temperature and fall-rate accuracies of the T-5 probes. The XBT temperatures averaged 0.07°C warmer than CTD temperatures, with some suggestion that the offset might be different for different acquisition acquisition systems and that it might be slightly temperature or pressure dependent. When the offset was removed, the differences between CTD and XBT temperatures had a standard deviation of about 0.08°C over a temperature range of 3°–29°C. An improved elapsed fall-time-to-depth conversion equation for Sippican T-5s in the Sargasso Sea was found to be z=6.705t−0.001619t2, with z the depth in meters and t the elapsed fall time of the probe in seconds. The standard deviation of depth was about 8 m over a depth range of 0 to approximately 1800 m. A cubic fit to the data was equally good or slightly bett...

Calculation of near-surface attenuation coefficients: the influence of wave focusing

The influence of small waves (<2 to 10 cm in height) in in-ground tanks on the vertical attenuation coefficient for downwelling irradiance (Kd) calculated from either the mean irradiances over a 5 minute run or the average of point-to-point measurements made at 10 and 20 Hz is investigated. Waves of mean frequencies of about 1 Hz were introduced in the tanks that produced corresponding frequencies in the power spectrum of measured irradiances. Coherence was greater than 0.7 between spectra of irradiance and waves when small waves were introduced, but was less than 0.3 under ambient conditions. Both increases and decreases in Kd values were observed when comparing Kd calculated from the point-to-point values and that obtained using the mean irradiances. When large waves (5-10 cm) were introduced, the methods deviated by up to a factor of two, presumably due to the large fluctuations in the point-to-point Kd values relative to the fluctuations in irradiance averaged over the 5 minute run. There were changes of 30% in Kd, calculated from mean irradiances, as wave height was increased.

Simple Methodology for Deriving Continuous Shorelines from Imagery: Application to Rivers

AbstractA methodology is developed to extract and process shoreline data, the interface between land and water, identified from imagery. Initially, image pixels containing water (water points) and pixel locations of the land/water interface (edge points) are extracted from an image using either a supervised, threshold approach or a newly developed, automated texture-based analysis. Both are described and demonstrated. Subsequently applied is a procedure for processing these edge and water point locations to obtain oriented and ordered shoreline coordinates. The described methodology has several advantages: (1) shoreline processing is independent of imagery source and resolution, that is, specification of search directions based on image resolution or desired shoreline resolution is unnecessary and (2) a need for additional postprocessing of remote-sensed data or extracted-edge data are obviated, that is, edge data need not be of high quality or vectorized. Details of the entire methodology, including algo...

Evaluation of the Sparton tight-tolerance AXBT

Abstract Forty-six near-simultaneous pairs of conductivity-temperature-depth (CTD) and Sparton “tight tolerance” air expendable bathythermograph (AXBT) temperature profiles were obtained in summer 1991 from a location in the Sargasso Sea. The data were analyzed to assess the temperature and depth accuracies of the Sparton AXBTs. The tight-tolerance criterion was not achieved using the manufacturers equations but may have been achieved using customized equations computed from the CTD data. The temperature data from the customized equations had a one standard deviation error of 0.13°C. A customized elapsed fall time-to-depth conversion equation was found to be z = 1.620t−2.2384 × 10−4 t2 + 1.291 × 10−7 t3, with z the depth in meters and t the elapsed fall time after probe release in seconds. The standard deviation of the depth error was about 5 m; a rule of thumb for estimating maximum bounds on the depth error below 100 m could be expressed as +12% of depth or +10 m, whichever is greater. This equation ga...