The paper describes an experimental set up used to collect GPS data in real time. The effect of weather of particular location is also considered in the paper. The major problems in GPS measurements may be due to tall buildings, high mountains, overhead foliage etc. The positioning data provided directly by the satellites are subject to variety of error sources such as thermal noise, tropospheric delays, multipath error, ephemeris errors, satellite clock errors and ionospheric delays before they are processed into position and time solution in the GPS receiver. The paper discusses DSP techniques such as Bad Data identification and modification and Kalman filter used to enhance the accuracy of GPS altitude measurements. Results obtained demonstrate that Kalman filter after Bad Data identification and modification technique significantly reduced the errors in GPS altitude measurements
