Broadband focal plane arrays, operating in UV-to-SWIR wavelength range, are required for atmospheric monitoring of greenhouse gases. Currently, separate image sensors are used for different spectral sub-bands: GaN for UV, Si for visible, and InGaAs for SWIR, requiring expensive component-level integration for hyper-spectral imaging. Also, the size of the InGaAs focal plane arrays is currently limited by the InP substrate area. We propose to develop a 640 x 512 UV-to-SWIR focal plane array sensor using GaAs substrate having following photodiode performance: (1) Cut-on Wavelength = 0.25 micron; (2) Cut-off Wavelength = 2.5 micron; (3) RoA > 35 Ohm-cm^2 at 300K; and (4) Quantum Eficiency > 30% in UV (0.25 to 0.4 micron), > 80% in Visible (0.4 to 0.9 micron), and > 70% in IR (0.9 to 2.5 micron) subbands. Based on P.I.'s experience on SCIAMACHY, this project will enable one image sensor for 8 spectroscopic channels currently orbiting on European Space Agency's ENVISAT.