One-Point Calibration for Soil Moisture Active/Passive (SMAP) L-Band Microwave Radiometer

The SMAP microwave radiometer's antenna temperature (TA) is computed from the radiometer outputs using a conventional two-point calibration method. The receiver's gain and noise temperature are calibrated using the internal reference load and internal noise diode. Then, the TA is derived. To provide an alternative to the current internal calibration approach for the SMAP L-band microwave radiometer and to determine the potential for reducing hardware for and cost of future projects, one-point calibration is studied. In this work, the internal reference load is used as the single source for one-point calibration, and the receiver noise temperature is modeled. The performance of the one-point calibration is validated by comparing the calibrated TAs, their uncertainties, and long-term calibration drifts to those of the conventional two-point calibration. Comparison results show that one-point calibration can achieve comparable performance, i.e., no larger than 0.07 K rms difference in calibrated TA, to the conventional two-point calibration. In addition, the long-term stability of the internal noise source is also included in the analysis.