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Introduction

RFlex was developed for research into the reflectance (water colour) of coastal seas. Using off -the-shelf spectroradiometers, a sensor pointing platform developed at the Finnish Environment Institute (SYKE), and a GPS module, it is made possible to collect reflectance data from moving vessels such as ferries or merchant vessels. The reflectance links in situ water quality data to basin-scale observations from satellite platforms.

RFlex hardware on R/V Aranda

Description

The software controls a stepper motor driver that turns the sensors to an optimum 135° from the solar azimuth, limited only by the free field-of-view from the mounting position on the ship. When mounted on one side of the bridge of a large ferry, it is possible to collect observations within a 90-135° angle (from solar azimuth) as long as the sun is not directly facing that side of the ship, and as long as the solar elevation exceeds the vertical viewing angle of the sensors. For sensors with an acceptance angle of 7 degrees mounted at a 42 degrees forward angle, this means solar elevation should be at least 42-7/2 = 38.5 degrees above the horizon, to avoid every possibility of looking at shadows cast by the ship.

The software can trigger sensor recordings and retrieve ascii data sent from three sensors which are typically set up to record downwelling irradiance (Ed), water-leaving radiance (Lw), and sky radiance (Ls). The software package that can be downloaded from our sourceforge page is set up to operate with TriOS RAMSES sensors because these are relatively affordable and offer sufficient sensitivity and resolution. In theory, adapting the relevant labview VI's to support communication protocols of other suppliers should be possible.

Data are written to a flat text file where every row is a new observation starting with all observation parameters including the sensor serial number (address), GPS position, viewing angle, ship speed, and a quality flag, followed by the uncalibrated sensor output.

Versions

See the version description page:
Rflex Hardware v1 / Software 0.3
Rflex Hardware v2 / Software 20130702 and up

Documentation

The latest function reference is found here. (needs update)
The latest building instructions is found in the Files section

Data processing

Algorithms for data processing and quality control of reflectance spectra have been published in the following paper, to download the source code of the algorithms refer to Git_fingerprint in the menu.

• Simis, S. G. H., and J. Olsson. 2013. Unattended processing of shipborne hyperspectral reflectance measurements. Remote Sensing of Environment 135: 202–212. doi: 10.1016/j.rse.2013.04.001 Link to open-access pdf

Acknowledgements

The initial development work was supported by EU FP7 projects PROTOOL and WaterS. PROTOOL is a Collaborative Project (Grant Agreement number 226880) co-funded by the Research DG of the European Commission within the RTD activities of the FP7 Thematic Priority Environment. WaterS "Strategic partnership for improved basin-scale Water quality parameter retrieval from optical Signatures" is a project funded by the European Union 7th Framework Programme under the People Programme, Marie Curie Industry-Academia Partnerships and Pathways (IAPP) scheme (call: FP7-PEOPLE-2009-IAPP)