Radiometers are a crucial element in NASA's studies of Planet Earth. This proposal addresses the basic need for a miniature light sensor, flexibly configurable and optimized for above and in-water optical property measurements. The innovation we are proposing develops a 1 cm diameter photodetector module, called a "microradiometer." The microradiometer consists of a photodetector, preamplifier with controllable gain, high resolution analog to digital converter (ADC), microprocessor, and an addressable digital port, all on one small, thin circuit assembly. We anticipate that the design will result in significant improvements in dynamic range, sampling speed, reliability, and reduced power consumption over existing instruments. In a Phase II embodiment, a single microradiometer forms the basis of a very small (much less than 2.5 cm diameter) single-channel submersible light sensor that can be deployed in support of coastal research opportunities. In another application, clusters of microradiometers can be matched with front end optics (collector/window/filter stack) to form small, fast, less expensive multiwavelength radiometers for a variety of measurements ? even hyperspectral applications. We call this configuration the Modular Microradiometer System (MMS). These MMS systems can be packaged into small underwater housings suitable for deployment on drifters, moorings, towed vehicles, and vertical profilers.