Abstract
An intercomparison of radiance and irradiance ocean color radiometers (The Second Laboratory Comparison Exercise—LCE-2) was organized within the frame of the European Space Agency funded project Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) May 8–13, 2017 at Tartu Observatory, Estonia. LCE-2 consisted of three sub-tasks: 1) SI-traceable radiometric calibration of all the participating radiance and irradiance radiometers at the Tartu Observatory just before the comparisons; 2) Indoor intercomparison using stable radiance and irradiance sources in controlled environment; and 3) Outdoor intercomparison of natural radiation sources over terrestrial water surface. The aim of the experiment was to provide one link in the chain of traceability from field measurements of water reflectance to the uniform SI-traceable calibration, and after calibration to verify whether different instruments measuring the same object provide results consistent within the expected uncertainty limits. This paper describes the activities and results of the first two phases of LCE-2: the SI-traceable radiometric calibration and indoor intercomparison, the results of outdoor experiment are presented in a related paper of the same journal issue. The indoor experiment of the LCE-2 has proven that uniform calibration just before the use of radiometers is highly effective. Distinct radiometers from different manufacturers operated by different scientists can yield quite close radiance and irradiance results (standard deviation s < 1%) under defined conditions. This holds when measuring stable lamp-based targets under stationary laboratory conditions with all the radiometers uniformly calibrated against the same standards just prior to the experiment. In addition, some unification of measurement and data processing must be settled. Uncertainty of radiance and irradiance measurement under these conditions largely consists of the sensor’s calibration uncertainty and of the spread of results obtained by individual sensors measuring the same object.
Highlights
Fiducial reference measurements of water reflectance are aimed to validate satellite data with requirement to provide metrological traceability to the SI units with related uncertainty estimates
This study aims to evaluate techniques and procedures needed for improvement of the traceability of the ocean color (OC) field measurements
For the RAMSES and HyperOCR this is achieved by three separate devices, while the WISP-3 contains three spectroradiometers integrated into a single device, and the SR-3500 uses a single spectrometer equipped with interchangeable entrance optics for irradiance and radiance
Summary
Fiducial reference measurements of water reflectance are aimed to validate satellite data with requirement to provide metrological traceability to the SI units with related uncertainty estimates These measurement uncertainties can arise from instrument specification, calibration and characterization, performance during field measurements due to various conditions of use and different targets, measurement protocol (including any corrections and assumptions), traceability of calibration sources to the primary SI standards. Intercomparison of data produced by a number of independent radiometric sensors measuring the same object can assess the consistency of different results and their estimated uncertainties depending on the type of the sensor, the spectrum of measured radiation, the environmental conditions, and the particular method used for collecting and handling the measurement data [1,2]. Small variability between individual sensors found during the current experiment confirms usefulness of the radiometric calibration performed at the same laboratory just before the comparisons
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
