NASA has teamed with the FAA, DoD, industry, and academia for research into the remote detection and measurement of atmospheric conditions leading to aircraft icing hazards. The ultimate goal of this effort is to provide pilots, controllers, and dispatchers sufficient information to allow aircraft to avoid or minimize their exposure to the hazards of in-flight icing. Since the hazard of in-flight icing is the outcome of aircraft flight through clouds containing supercooled liquid water and strongly influenced by the aircraft's speed and configuration and by the length of exposure, the hazard can't be directly detected, but must be inferred based upon the measurement of conducive atmospheric conditions. Therefore, icing hazard detection is accomplished through the detection and measurement of liquid water in regions of measured sub-freezing air temperatures. The icing environment is currently remotely measured from the ground with a system fusing radar, lidar, and multi-frequency microwave radiometer sensors. Based upon expected ice accretion severity for the measured environment, a resultant aircraft hazard is then calculated. Because of the power, size, weight, and view angle constraints of airborne platforms, the current ground-based solution is not applicable for flight. Two current airborne concepts are the use of either multi-frequency radiometers or multi-frequency radar. Both ground-based and airborne solutions are required for the future since ground-based systems can provide hazard detection for all aircraft in airport terminal regions while airborne systems will be needed to provide equipped aircraft with flight path coverage between terminal regions.
Abstract. Radio-frequency interference (RFI) can significantly contaminate the measured radiometric signal of current spaceborne L-band passive microwave radiometers. These spaceborne radiometers operate within the protected passive remote sensing and radio-astronomy frequency allocation of 1400-1427 MHz but nonetheless are still subjected to frequent RFI intrusions. We present a unique surfacebased and airborne hyperspectral 385 channel, dual polarization, L-band Fourier transform, RFI-detecting radiometer designed with a frequency range from 1400 through ≈ 1550 MHz. The extended frequency range was intended to increase the likelihood of detecting adjacent RFI-free channels to increase the signal, and therefore the thermal resolution, of the radiometer instrument. The external instrument calibration uses three targets (sky, ambient, and warm), and validation from independent stability measurements shows a mean absolute error (MAE) of 1.0 K for ambient and warm targets and 1.5 K for sky. A simple but effective RFI removal method which exploits the large number of frequency channels is also described. This method separates the desired thermal emission from RFI intrusions and was evaluated with synthetic microwave spectra generated using a Monte Carlo approach and validated with surface-based and airborne experimental measurements.
Abstract. Radio Frequency Interference (RFI) can significantly contaminate the measured radiometric signal of current spaceborne L-band passive microwave radiometers. These spaceborne radiometers operate within the protected passive remote sensing and radio astronomy frequency allocation of 1400–1427 MHz, but despite this are still subjected to frequent RFI intrusions. We present a unique surface-based/airborne hyperspectral 385 channel, dual polarization, L-band Fourier transform, RFI detecting radiometer designed with a frequency range from 1400 through ≈ 1550 MHz. The extended frequency range was intended to increase the likelihood of detecting adjacent RFI-free channels to increase the signal, and therefore increase the thermal resolution, of the radiometer instrument. The external instrument calibration uses three targets (sky, ambient, and warm) and validation from independent stability measurements shows a mean absolute error (MAE) of 1.0 K for ambient and warm targets, while the MAE is 1.5 K for sky. A simple but effective RFI removal method which exploits the large number of frequency channels is also described. This method separates the desired thermal emission from RFI intrusions, and was evaluated with synthetic microwave spectra generated using a Monte Carlo approach and validated with surface-based and airborne experimental measurements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.