An In-Situ GPS Reference is being pursued by the National Weather Service for independent measurements/calculations of geometric heights, geo-potential heights, derived-pressures, and the u- and v-components for calculating winds aloft. NWS is interested in the development for an in situ (GPS) referencing system (ISRS) -- effectively a balloon-borne differential GPS reference akin to a surface-based one used with continuously operating reference stations (CORS) -- to validate GPS measurements from balloon-borne systems. In the past, for example, validation of radiosonde GPS measurements required very costly tests at places like the White Sands Missile Range with payloads requiring special permission for lifting a very heavy apparatus aloft on a NASA-style helium balloon. With today's technological leaps, a similar low-cost package could be developed and implemented as an independent reference meeting several objectives as follows: Integration of a very accurate GPS engine with a balloon-borne telemetry system capable of measuring positional accuracies to +/- 1-meter; transmission of GPS positional data in a form acceptable for reprocessing using CORS; and developing an interface between this package and a commercial-off-the-shelf ground system to process the results to the customer. The benefits of this research include the development of a new in situ reference standard, which doesn't exist today, that can assist both government and non-government customers, e.g., radiosonde vendors, in assessing their balloon-borne GPS instrumentation and verifying performance of their measurements. Thus the federal government would be establishing this new reference standard. The technological gap being filled with this research is centered on the advanced GPS technology to extend the CORS reference platform from the surface up to 35 kilometers aloft! The end goal would be a balloon-borne GPS reference package interfaced to a radiosonde/ground system with open source software, commercially available. As more and more applications requiring accurate GPS are flown aloft, this reference technology will play an even bigger, and possibly, pivotal role in ensuring excellent agreement of the relative and absolute accuracies of the GPS-engines. A full description of the NWS plan for the development and application of this method will be discussed in the extended abstract.