A radar apparatus for detecting a distance/velocity has a transmitting system for transmitting a signal which is frequency-modulated with a modulating signal having a predetermined recurrence frequency, a receiving system for receiving a reflected wave signal, which is the modulated transmission signal transmitted from the transmitting system and reflected by an object, and which mixes the reflected wave signal and the modulated transmission signal from the transmitting system so as to detect a beat wave signal of the reflected wave signal and the modulated transmission signal. The apparatus also includes a high-pass filter for filtering the beat wave signal detected in the receiving system so as to cut off modulation frequency components of the modulated transmission signal with orders that are equal to or lower than a predetermined order, and a distance/velocity calculating unit which calculates the distance to and the relative velocity with respect to the object based on frequency information in the beat wave signal which has been passed through the high-pass filter. Accordingly, the radar apparatus effectively removes FM/AM conversion (reconversion) noise in a simple structure thereby to accurately detect the distance to and the relative velocity with respect to the object even with low transmitting power.

A radar altimeter system uses a microprocessor-based subsystem to process radar signals in software. The subsystem includes a track loop and a verify loop for digital signal processing of the radar signals. The track loop generates a gate pulse and integrates a radar return signal over the time window defined by the gate pulse in order to determine the leading edge of the return pulse. The verify loop positions the gate pulse for maximum overlap with the return pulse and integrates the return pulse over the gate pulse to determine the maximum signal strength of the radar return signal.

A distance measurement apparatus includes a transmitting device for transmitting a forward electromagnetic wave. A receiving device operates for receiving an echo wave caused by reflection of the forward electromagnetic wave at an object, and converting the received echo wave into a first received signal. A scattered-wave detecting device operates for detecting a scattered wave reaching the receiving device and caused by reflection of the forward electromagnetic wave at an obstacle which occurs prior to the reflection of the forward electromagnetic wave at the object. A cancel-signal generating device operates for generating a cancel signal to cancel a scattered-wave-corresponding component of the first received signal generated by the receiving device in response to the scattered wave detected by the scattered-wave detecting device. A scattered-wave canceling device operates for removing the scattered-wave-corresponding component from the first received signal in response to the cancel signal generated by the cancel-signal generating device to change the first received signal to a second received signal. A distance calculating device responsive to the second received signal operates for measuring a time interval between a moment of the transmission of the forward electromagnetic wave by the transmitting device and a moment of the reception of the echo wave by the receiving device, and calculating a distance to the object on the basis of the measured time interval.

In an FM-CW radar system, a beat signal is frequency-analyzed for selecting ascending-side beat frequencies and descending-side beat frequencies for a plurality of targets. By pairing the ascending-side and descending-side beat frequencies one by one from each side, all possible combinations thereof are prepared. Based on these beat frequency combinations, beat frequency combinations after a given time are predicted, respectively. If an ascending-side beat frequency and a descending-side beat frequency of the predicted beat frequency combination are found in ascending-side beat frequencies and descending-side beat frequencies of a beat signal selected after the given time, respectively, or in the neighborhood of them, respectively, the predicted beat frequency combination of the found ascending-side and descending-side beat frequencies is set as a correct beat frequency combination. A further correct beat frequency combination/combinations can be set in the same manner. Based on these correct beat frequency combinations, information about the targets can be correctly achieved.

An altitude measuring system and method for aircraft is provided. The altitude measuring system includes altitude sensors for providing data to an altitude processing unit. The altitude processing unit spatially averages each output to determine a mean altitude. Pitch and roll are accounted for by correction. A method of determining aircraft altitude from a plurality of altitude sensors includes receiving altitude sensor data from each sensor and spatially averaging the altitude sensor outputs to determine aircraft altitude. A method of estimating the maximum height of an ocean surface includes receiving a plurality of altitude sensor data and determining a mathematical description of the ocean surface from the sensor data. The maximum probable wave height of the ocean surface is estimated from the mathematical description. From the maximum wave height, a cruise altitude may be determined.