Abstract
This manuscript first revises the performance of total power, Dicke-type and noise-injection microwave radiometers. Equations for the radiometric resolution are revised or derived, and their performance in terms of the radiometric resolution improvement with respect to the ideal total power radiometer resolution is evaluated. It is then shown that the radiometric resolution of noise-injection radiometers can be optimized by adjusting dynamically the integration times devoted to the three measurements: antenna, antenna plus noise, and reference load. Numerical results are then presented to illustrate the dependence of the radiometric resolution with different instrument parameters. Experimental results are finally presented to corroborate the predicted performance. It is also shown that in many cases of interest these integration times can be set to a constant value with little degradation with respect to the optimum case, but better than the case in which the total integration time is divided in three equal subintervals.
Highlights
Review of Radiometer Topologies, Stability, and Radiometric Resolution ConsiderationsMicrowave radiometers are used in a number of Earth Observation applications
Its performance has not been optimized in terms of stability or radiometric resolution, but rather, it tries to show the different performances in different operation modes
The radiometer‘s topology is shown in Figure 5 and it can be operated as a NIR, a Dicke, or a TPR
Summary
Microwave radiometers are used in a number of Earth Observation applications. For each application, the spatial resolution (determined by the size of the projected beam), the radiometric. The input is modulated using an input switch (the Dicke switch) to commute between the antenna and a matched load at a known and stable physical temperature (TREF), while at the same time, the output is demodulated by synchronously multiplying the detected signal by 1 before the low-pass filter that acts as integrator (Table 1b). With this technique, and provided the switching rate (fs) is much higher than the bandwidth of the gain fluctuations‘ spectrum, so that ΔG G f m?f ΔG G f , the impact of gain fluctuations in s the radiometric resolution is minimized [5]: T=. BLPF e) Balanced Dicke radiometer by reference channel d) Balanced Dicke radiometer by gain modulation c) Balanced Dicke radiometer by duty cycle modulation b) Dicke radiometer (unbalanced)
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