The Green-house gas Observation SATellite (GOSAT) was launched to determine the continental CO2 inventories. Its sensor is based on a passive remote sensing technique developed to achieve less than 1% relative accuracy for atmospheric CO2 measurements. Meanwhile, a laser remote sensor with the differential absorption spectrometry has been developed for a candidate of a future space-based mission to observe the atmospheric CO2 or other trace gases. A prototype of the newly developed active remote sensor has been performed to demonstrate a properly validated performance for ground-based and airborne systems. This study shows the results of the in-house and field measurements. The in-house measurement demonstrated the linearity with the correlation coefficient of over 0.99 between the instrumental response and the known CO2 density in the cell. The diurnal variation obtained from our system is consistent (correlation coefficient of 0.95) with that of multi-positioned in situ sensors, indicates the spatial responsibility of the atmospheric CO2 obtained from our remote sensor with two ~3-km observation paths.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.