As the radar beam travels out at an angle, the radar beam travels higher in the atmosphere. By the time the radar beam is 50 miles from the radar site, the radar beam is 5,000 feet up in the air. Then you look at a radar image, and it doesn’t show snow at your location.

What’s harder to detect than light rain? Light snow. That’s because snow doesn’t reflect radar beams as strongly as rain.

In addition, precipitation particles are big enough to reflect microwaves, whereas cloud particles aren’t. Hence, weather radars can detect precipitation but can’t see clouds at all. (This makes weather-radar maps excellent complements to weather-satellite images, which can show cloud tops but not precipitation.)

Flocks of birds are certainly detectable on radar, although filtering software is designed to exclude relatively slow-flying and low-altitude objects.

Abstract: Human detection using sensors preserves the privacy. The Passive Infrared (PIR) sensor is used to detect the presence of human. But this detects the human only if they are in motion.

PRT is also equal to the sum, PRT = PW+RT. PRF = pulse repetition frequency. PRF has units of time-1 and is commonly expressed in Hz (1 Hz = 1/s) or as pulses per second (pps). PRF is the number of pulses transmitted per second and is equal to the inverse of PRT.

From 15,000 ft. it can detect aircraft and even vessels all of the way down to the surface of the ocean out to 200 miles. In civil aviation, mountains or other terrain can block radar signals. Going too low in a mountainous area will take you out of their radar coverage.

Flying low will not avoid detection with modern radars; instead latest generation of military aircraft use stealth technology and active radar jammers to avoid being detected by radar systems.

Helicopter NOE flying Attack helicopters can hide behind trees or buildings, “popping up” just enough to use their (rotor mast-mounted) radar or other sensors and then minimally exposing themselves to launch weapons.