DUAL K AND C BAND TRANSPONDER FOR SATELLITE ALTIMETRIC CALIBRATION

WE PROPOSE TO INVESTIGATE TECHNIQUES TO MAKE A DUAL FREQUENCY (K-BAND AND C-BAND) TRANSPONDER THAT WILL SIMULATE THE SAME SURFACE REFLECTION OF RANGING PULSES TRANSMITTED FROM THE TOPEX/POSEIDON SPACECRAFT. THUS, THE TRANSPONDER MUST RECEIVE AND TRANSMIT ON THE SAME FREQUENCIES. THEREFORE, IT MUST RECEIVE THE SPACECRAFT TRANSMISSIONS AND DETERMINE THEIR CHARACTERISTICS, IN ORDER TO TRANSMIT REPLICAS AT THE SAME TIME THEY WILL HAVE BEEN REFLECTED. MATCHED FILTER SURFACE ACOUSTIC WAVE (SAW) CORRELATION DETECTION WILL ENABLE THE GENERATION OF CHIRP REPLICAS OF VERY HIGH PRECISION. BECAUSE THE TRANSPONDER IS ACTIVE, THE RETRANSMITTED CHIRPS WILL UNDERGO ONLY R(2) POWER LOSS RATHER THAN THE R(4) LOSS ASSOCIATED WITH COMPETING SYSTEMS. THESE HIGH POWER RETURNS WILL FORCE TOPEX TO TRACK THE TRANSPONDER FOR CALIBRATION AND ORBIT DETERMINATION. THE TRANSPONDER WILL USE THE SPACECRAFT EPHEMERIS AND KNOWN LOCATION OF THE TRANSPONDER TO GREATLY IMPROVE THE SPEED AND ACCURACY WITH WHICH IT CAN LOCK ONTO THE SPACECRAFT TRANSMISSIONS. THIS STUDY WILL RESULT IN THEDESIGN OF A DEVICE THAT WILL PROVIDE NASA THE CAPABILITY TO ESTABLISH AND MAINTAIN SEA SURFACE TRUTH FOR SATELLITE ALTIMETER VALIDATION. THE TRANSPONDER COULD ALSO BE USED TO MONITOR GROUND SURFACE SUBSIDENCE.