Performance Demonstration Statement Satlantic ISUS V3 Nitrate Sensor.

Abstract

In this Demonstration Statement, we present the performance results of the Satlantic ISUS V3 under diverse environmental conditions in surface mapping, depth profiling and moored deployment field tests. A total of three different field sites were used for testing, including estuary, open-ocean, and riverine environments. For the surface mapping deployment in Monterey Bay, the ISUS nitrate estimates closely tracked ambient nitrate concentrations (ISUS:Reference Sample = 1.04 ±0.2) over a two -order magnitude range and all expected data were reported. The ISUS successfully reported out nitrate concentrations at a 1 Hz sampling rate over two vertical p rofiling tests. Agreement with field reference sample concentrations was generally good, but a calibration offset was apparent from direct comparisons. The ISUS was successfully tested in a moored application at two of the three attempted test sites. A mechanical failure of the battery pack was encountered in the Michigan mooring test and no data were collected. All expected data were reported out from the other two mooring test sites in Chesapeake Bay, MD and Resurrection Bay, Alaska. In the Chesapeak e Bay test the ISUS in situ measurements showed good overall agreement with reference samples (R 2 = 0.8) but reported concentrations were positively biased at a ratio of around 2.1 times laboratory measured concentrations. In Resurrection Bay, AK the response of the ISUS was more variable, but within its specified accuracy of 2 μM, and had a similar overall positive bias of 2.3 times laboratory measured concentrations. During the last 10 days of the AK deployment the ratio of instrument:reference samples improved to a mean ratio of 1.4. Exposure to both nitrate and nitrite samples singularly and in mixtures shows that while the ISUS responds to the presence of nitrite in either pure solution or mixtures that the calibrated optical algorithms provided with the instrument produce accurate estimates of nitrate in mixed standard solutions at similar molar ratios, as well as, in ambient waters where nitrite is typically less than 10% of nitrate concentrations. We encourage readers to review the entire document for a comprehensive understanding of instrument performance and to discuss results with the instrument manufacturer. The application of any post-test corrections to the data and the manufacturer’s interpretation of the test results are presented in Appendix 1. In general, the ISUS V3 demonstrated the capability to successfully measure in situ nitrate concentrations under a variety of field conditions and in multiple sampling applications.