The digital array gas radiometer (DAGR) is a new sensor design for accurate measurement and monitoring of trace gases in the boundary layer from space, aircraft, or ground-based platforms using scattered sunlight. Target gases include CH4, CO, CO2, N¬2O and other species critical to climate science, environmental monitoring and commercial pollution compliance efforts. The DAGR approach builds on traditional gas-filter correlation radiometry (GFCR), a well-known and proven technology for trace gas sensing. The effectiveness of GFCR, however, has historically been limited in downlooking applications primarily because variations in surface albedo degrade its performance. In our Phase I effort, we investigated and demonstrated the ability of the DAGR design to overcome these limitations. With the successful completion of these feasibility studies, the technology has been increased to TRL-3. In the Phase II effort, we will construct and test a prototype DAGR sensor for CH4 detection and monitoring, advancing the technology to TRL-5. CH4 was chosen as our target gas to meet the pressing commercial need for an improved natural gas leak detection system. For NASA, the DAGR prototype will significantly advance the technology needed for future missions such as ASCENDS, GEOCAPE, and GACM. DAGR represents a major advance in using backscattered light for detecting concentrations of key molecular species.