The pressure altitudes that have been archived in the general RAF C-130 data set use a standard altitude reference pressure and temperature of 1013.246 mb, 288.15K. This often leads to pressure altitudes during flight that are inaccurate, particularly during low level legs over the ocean. The research radar altimeter was not operatioal during ACE-1 so pressure altitude is the only measure of altitude that we have. We have now reprocessed Flights rf3-rf30 and corrected the pressure altitude. The pressure altitude is being calculated by PALTC = (Tr/gamma)[1-(P/Pr)^X], where Tr and Pr are sea level values of temperature and pressure, gamma is the standard lapse rate , and X is R*gamma/g, where R is the universal gas constant for dry air, and g is the acceleration of gravity. Rather than use a single reference temperature and pressure, we use the temperature and pressure at takeoff and landing as two reference points (Anchorage, Honolulu, Xmas Island, Fiji, Christchurch and Hobarth were all nearly at sea level +- 5 m). We then found all flight legs that were flown at 100, 300 or 500 ft and determined the altimeter setting (surface pressure) at these points using the transform PSURF = P*exp(g/R(HGM/Tbar) where P is the pressure at the flight altitude, g and R are as defined above, HGM is the altimeter reading from the pilots radar altimeter, and Tbar is the average temperature between surface and flight altitude. The surface temperature was assumed to be the ocean temperature determined by the Heinmann thermometer and flight level temperature was taken from the radome right Rosemount probe. The pilots had a working radar altimeter so we know the low level flight legs fairly precisely, at least within +-5 m. We interpolate linearly between all the surface pressures to get estimates between the reference points. These are then used in the corrected calculation of pressure altitude given above. A major caution: Whereas we think that these new pressure altitudes are much more accurate than the original values, there still will be some uncertainties that result from the assumption of a standard lapse rate. The values close to the surface will be most accurate and the uncertainty will increase with increasing altitude. The lidar data are presently being processed to determine aircraft altitude when the lidar is pointing downward. These will be the most accurate height data, once processed, and will be used to ascertain the accuracy of the corrected pressure altitudes. In the meantime, we are reluctant to place an uncertainty estimate on the corrected altitude values. We are probably safe in saying that within the boundary layer, the corrected altitudes are acccurate to within +- 25m.