||An underwater radiometer designed for multiwavelength profiling and surface measurements of irradiance, radiance, temperature, and remote sensing reflectance in the SeaWiFS wavelength bands. The standard instrument comes with 8 (expandable to 13) channels each of downwelling irradiance and upwelling radiance (or optionally, irradiance), a spectral range of 340-780nm, a depth transducer (200m full scale, 500m optional) and a dual axis inclinometer. The optical sensors are based on high stability, solid-state photodetectors, each with its own narrow-band (10 nm) interference filters. Additional, externally-mounted blocking filters are used where needed. The irradiance sensor is composed of an array of detectors that view a common cosine-corrected optical collector. The radiance sensor is a constructed from an array of telescopes, which define the collection angle (10° field of view), and are coupled to individual detectors. Each detector is connected to an electrometer amplifier, forming an array of amplifiers that are scanned under microprocessor control at approximately one channel per millisecond. The instrument can be modified to measure ultraviolet radiance and irradiance, vector (cosine) upwelling irradiance, and scalar upwelling and downwelling irradiance. A variety of additional sensors can be added to the MER-2040A to form a CTD with auxiliary sensors. Options include PAR, fluorescence, water current, transmissance, temperature, conductivity, oxygen and high resolution pressure sensors.