Performance Verification Statement for the McVan Analite NEP395 Turbidity Probe.

Abstract

Instrument performance verification is necessary so that effective existing technologies can be recognized and so that promising new technologies can become available to support coastal science, resource management, and ocean observing systems. The Alliance for Coastal Technologies (ACT) has therefore completed an evaluation of in situ turbidity sensors. Turbidity is a property commonly used to describe water clarity in both marine and freshwater environments, providing a gross assessment of the amount of suspended material. Differences in methods of measurement and their individual responses to varying types of suspended material have made the measurement of turbidity difficult to perform in a consistent and standardized way. This has necessitated many public-service agencies to define turbidity in very specific terms based on optical methods of measurement. Despite these limitations, a variety of in situ instruments that provide some measure of turbidity are commonly and successfully used in many researcher and monitoring settings as a relative measure of suspended sediment concentration. As described below in more detail, field tests that examine manufacturers’ turbidity values against simultaneously determined measurements of transmissivity, total suspended solids, and particulate organic carbon were designed only to examine an instrument’s ability to track changes in water clarity through time and NOT to determine how well the instrument’s values directly correlated with the ancillary measurements. The use of turbidity sensors to estimate a specific parameter (such as TSS) in nature requires local calibration to take into account many factors including particle composition, size and shape, along with other any other light scattering influences from dissolved organic compounds. In this Verification Statement, we present the performance results of the McVan Analite NEP395 Turbidity Probe evaluated in the laboratory and under diverse environmental conditions in moored field tests. A total of seven different field sites were used for testing, including tropical coral reef, high turbidity estuary, open-ocean, and freshwater lake environments. Because of the complexity of the tests conducted and the number of variables examined, a concise summary is not possible. We encourage readers to review the entire document for a comprehensive understanding of instrument performance.