This paper presents design details of SEAL, a general-purpose low-cost spatial-temporal data logger. The SEAL module includes GPS, Lithium-ion polymer battery, high-density flash memory and a USB interface. The main features include: low cost, very large size XML-based data logs, low power consumption, flexible sensor attachment, and an optional Wi-Fi interface for Internet-enabled data. It is compact, self-contained and light-weight—suitable for a UAV (unmanned aerial vehicle) payload. In fact, our general-purpose SEAL module can turn any mobility platform into a mobile sensor. For example, we have interfaced CO2 and NH3 sensors with a SEAL module and attached the pack to a car which can be driven to map the CO2 and NH3 in a region of interest. The XML-based data logs allow interoperable post-processing in every modern computer operating system and display in desktop mapping applications such as Google Earth and NASA WorldWind.