Detailed aeroheating information is critical to the successful design of a thermal protection system TPS for an aerospace vehicle. This report describes NASA Langley Research Center's LaRC two-color relative-intensity phosphor thermography method and the IHEAT software package which is used for the e cient data reduction and analysis of the phosphor image data. Development of theory is provided for a new weighted two-color relative-intensity uorescence theory for quantitatively determining surface temperatures on hypersonic wind tunnel models; an improved application of the one-dimensional conduction theory for use in determining global heating mappings; and extrapolation of wind tunnel data to ight surface temperatures. The phosphor methodology at LaRC is presented including descriptions of phosphor model fabrication, test facilities and phosphor video acquisition systems. A discussion of the calibration procedures, data reduction and data analysis is given. Estimates of the total uncertainties with a 95 con dence level associated with the phosphor technique are shown to be approximately 8 to 10 percent in the Langley's 31-Inch Mach 10 Tunnel and 7 to 10 percent in the 20-Inch Mach 6 T unnel. A comparison with thin-lm measurents using two-inch radius hemispheres shows the phosphor data to be within 7 percent of thin-lm measurements and to agree even better with predictions via a LATCH computational uid dynamics solution CFD. Good agreement between phosphor data and LAURA CFD computations on the forebody of a vertical takeo vertical lander con guration at four angles of attack is also shown. In addition, a comparison is given between Mach 6 phosphor data and laminar and turbulent solutions generated using the LAURA, GASP and LATCH CFD codes. Finally, the extrapolation method developed in this report is applied to the X-34 con guration with good agreement b e t w een the phosphor extrapolation and LAURA ight surface temperature predictions. The phosphor process outlined in the paper is believed to provide the aerothermodynamic community with a valuable capability for rapidly obtaining 4 to 5 weeks detailed heating information needed in TPS design.