Optical detectors for integration into a low cost radiometric device for in-water applications: A feasibility study

Abstract

Higher water temperatures and nutrient loads, along with forecasted climate changes are expected to result in an increase in the frequency and intensity of eutrophication-linked algal blooms (Bernard, 2010, unpublished). The destructive impact such phenomena have on marine and freshwater systems threaten aquaculture, agriculture and tourism industries on a global scale (Bernard, 2010, unpublished). An innovative research project, Safe Waters Earth Observation Systems (SWEOS) proposes the use of space-based remote sensing techniques, coupled with in-situ radiometric technology to offer a powerful and potentially cost effective method of addressing algal bloom related hazards. The work presented in this paper focuses on the decision making processes involved in the development of autonomous bio-optical sensors whose purpose includes, but is not limited to; water constituent monitoring, satellite calibration validation and ocean colour satellite product matchups. Several criteria including cost, optical throughput, linearity and spectral sensitivity were examined in an attempt to choose the detector best suited for its intended application. The CMOS based module tested in the laboratory experiments that was found to have produced the best performance-cost ratio was chosen for integration into the in-water radiometric device built and tested at the Council for Scientific and Industrial Research (CSIR) (Ramkilowan et al. 2012, unpublished). Mass production of this prototype technology will commence, pending data quality comparable to that of an already calibrated, in-water radiometer; to be tested at field trials in Elands Bay (32°17'45.82 S; 18°14'44.45 E), Loskop Dam (25°27'15.25 S; 29°17'28.21 E) and Saldanha Bay (33° 3'11.38 S; 17°59'54.29 E).