The proposed project will develop a lightweight, low volume and low power consuming sensor for accurate measurements of liquid water or ice water content of clouds, water vapor concentration and local thermodynamic state of the atmosphere. It will be capable to operate from a small unmanned aircraft system platform, with instrument weight less than 6 kg and power requirement of less than 150W. The observations of the Profiling Airborne Microwave Radiometer will improve understanding and representations of clouds in the climate and Earth system models, as well as their interaction and coupling with the Earths surface. Commercial application of this technology can significantly improve weather observation and thus local short term weather forecasts. Boulder Environmental Sciences and Technology will develop an advanced, compact, low power and integrated radiometer receivers. These receivers, the heart and the most expensive part of a radiometer, will be integrated into an airborne radiometer system that could be installed on a small unmanned aircraft system platform. The Profiling Airborne Microwave Radiometer will operate autonomously and it will depend on an aircraft only for power. The instrument overall preliminary design will be finalized during Phase I. Two filters for the proposed direct detect radiometer receivers, a critical technology for overall instrument development success, will be designed, manufactured and bench tested. The development of filters that are easy to integrate and have proper characteristics for a radiometer operation will allow higher level of instrument integration and thus overcome significant limitations of current technologies. According to a study of the U.S. Department of Transportation there will be ~250,000 unmanned aerial systems within the U.S. airspace by 2035, of which ~175,000 will be in the commercial market place. The widening of the commercial use of drones will increase the demand for sensors, capable of operations on these platforms. One of the important and obvious application are in observations of a local weather. Such observations can improve the accuracy of severe storms warnings and improve local, short term weather forecast. Any business whose operations depend on the weather will benefit from improved forecast. Such businesses are agricultural, airports, seaports, renewable energy producers, electrical utilities, shipping companies, skiing resorts, search and rescue providers, and others. A novel technology for integration of microwave radiometers will be developed. It will enable a development of a small, low power, weather sensor for operation on a drone. A preliminary design of a new miniature sensor for improved weather observation, important for agricultural, aviation, renewable energy, and other businesses, will be developed during Phase I.