This paper describes the design, construction and testing of a delay/Doppler-mapping receiver (DDMR) that was specially designed for gathering and processing Global Positioning System (GPS) reflected signals for earth remote sensing. The DDMR can process GPS L1-C/A signals received directly and after reflection, and compute complexvalued cross correlations of GPS L1-C/A reflected signals as well as navigation solutions acquired from direct signals in real time. The outputs of the DDMR can be used for altimetry applications, soil moisture measurement, ice characterization and ocean state retrieval, and other future applications. This paper presents the DDMR hardware architecture, signal processing issues and some preliminary experiment results.