Protocols for Verifying the Performance of In Situ Salinity Sensors.

Abstract

his ACT Technology Evaluation will examine individual sensor performance both in the laboratory and across different field conditions in moored and vertically profiled applications. We will focus specifically on commonly used inductive, conductive, and electrode based conductivity sensors with measuring ranges from 0 - 100 mS/cm. For those instruments that do not internally derive salinity values, we will the use the practical salinity scale approach using the formulas supplied in UNESCO Technical Memo by Fofonoff and Millard (1983). These derived salinity values will be reported without units per recommendations of the International Oceanographic community (reference). 3. Objectives and Focus of Salinity Sensor Performance Verification The fundamental objectives of this Performance Verification are to: (1) highlight the potential capabilities of in situ salinity sensors by demonstrating their utility in a broad range of coastal environments with varying salinity, (2) verify manufacturer claims on the performance characteristics of commercially available salinity sensors when tested in a controlled laboratory setting, and (3) verify performance characteristics of commercially available salinity sensors when applied in real world applications in a diverse range of coastal environments. ACT has performed a customer needs and use assessments and held a technology workshop on in situ salinity sensors. As part of these reviews, scientists, resource managers, and other users of these technologies were asked about their current use or application of these instruments, their perceptions of limitations or problems with the technology, and the most important criteria they use when selecting a sensor or instrument package . The results of these assessments were used to identify the main applications and key parameters that ACT will evaluate in this Technology Verification. The two most common applications for users of salinity sensors were moored deployments on remote platforms for continuous monitoring and vertical profiling using CTD/ rosette platforms. The use of salinity sensors among our survey respondents was evenly divided between freshwater, brackish water, and marine environments, but with over 75% of the respondents indicated use within shallow, nearshore environments. The greatest use of salinity data was to provide a general description of the environment, followed by identification of water masses and making density calculations for stratification. Approximately 40% of the respondents stated an accuracy requirement of 0.1 salinity, while another 30% stated a requirement of 0.01 salinity. The performance characteristics that ranked highest included reliability, accuracy, precision, ease of calibration, and stability. This ACT Performance Verification will focus on these types of applications and criteria utilizing a series of field tests at up five of the ACT Partner Institution sites, representing marine, estuarine and freshwater environments. A laboratory component of the Verification will be performed at a sixth Partner Institutional site. Complete needs and use assessment and workshop reports can be found at www.act-us.info