Eliminating range folding error in doppler radar returns

Asked by: Stephanie Walker

What causes range folding?

range_folding. Range folding takes place when a radar echo from outside the radar’s maximum unambiguous range gets displayed incorrectly within the radar range: The maximum unambiguous range is determined by the PRF (pulse repetition frequency).

What are the factors affecting range resolution of a radar?

Range resolution is the ability of a radar system to distinguish between two or more targets on the same bearing but at different ranges. The degree of range resolution depends on the width of the transmitted pulse, the types and sizes of targets, and the efficiency of the receiver and indicator.

What is the range of Doppler radar?

Pulse-Doppler typically uses medium pulse repetition frequency (PRF) from about 3 kHz to 30 kHz. The range between transmit pulses is 5 km to 50 km. Range and velocity cannot be measured directly using medium PRF, and ambiguity resolution is required to identify true range and speed.

What does dBZ mean in radar?

decibels

The colors represent the strength of returned energy to the radar expressed in values of decibels (dBZ). The color scale is located at the lower right of each image. As dBZ values increase so does the intensity of the rainfall. Value of 20 dBZ is typically the point at which light rain begins.

What causes range ambiguity?

In Synthetic Aperture Radar (SAR) imaging, range ambiguity is caused by the echoes of the previous and latter transmitted pulses scattered from undesired range zones [1].

How do PRF can minimize ambiguity in range?

Abstract. The range ambiguity resolution for high ‘PRF pulse-Doppler radars can be resolved using a simple algorithm based on residue arithmetic. The unambiguous range is found from R = T + R(a), where T is the output of a look-up table and R(a) is one of the measured ambiguous ranges.

How can I improve my radar range resolution?

The good range resolution performance is required in radar system to detect small targets at a long distance. It is already known that the longer pulse will increase energy and improve target detection. Conversely, shorter pulse will increase the range resolution of radar.

How we can increase the range of a radar?

Range capabilities of the radar increase with peak power. Doubling the peak power increases the range capabilities by about 25 percent. The longer the pulse length, the greater is the range capability of the radar because of the greater amount of energy transmitted.

What is range accuracy in radar?

Practically, the accuracy depends on the size of the individual range-cells in signal processing. ICAO recommends[3] a range cell size of 1/128 NM, i.e. about 14.5 m, for air traffic control air surveillance radar, which corresponds to a time interval of almost 10 nanoseconds.

What is a range Doppler response?

If a transmitter platform is stationary, a range-Doppler map shows a response from stationary targets at zero Doppler. For targets that are moving relative to the transmitter platform, the range-Doppler map shows a response at nonzero Doppler values.

What is range Doppler coupling?

The radar accuracy is affected by range–Doppler coupling, which yields a displacement in the measured range proportional to the target radial velocity, i.e., the Doppler shift in the returned pulse. Although in oceanography this effect is usually not accounted for, its relevance grows in ship detection.

What is range Doppler algorithm?

RCMC is performed in. range frequency and azimuth frequency domain. Since, azimuth frequency is affected by. Doppler Effect and azimuth frequency is bonded with Doppler frequency, it is called. Range Doppler Algorithm.

How is range ambiguity artifact eliminated?

The easiest way to reduce RAAs is to change the image depth. Sufficient knowledge of RAAs can prevent misdiagnosis of erroneously displayed returning echoes as real pathologic changes. Keywords: Gallbladder; Liver; Range-ambiguity artifact; Ultrasound; Urinary bladder.

How do you increase maximum unambiguous range?

To extend the maximum unambiguous range, the PRI needs to be enlarged so that the echoes reflected by farther targets can be received. However, the uniform under-sampling method that directly reduce the PRF results in heavy Doppler aliasing.

What is unambiguous range in radar?

The unambiguous range of a radar is the maximum range at which a target can be located so as to guarantee that the reflected signal/pulse from that target corresponds to the most recent transmitted pulse.

On which factor the maximum range of radar depends?

Since R_max ∝ D^1/2, If the antenna aperture is doubled i.e. if the diameter is doubled, the radar range will be increased by √2.

How is radar range of resolution calculated?

Range resolution as a distance can be calculated as follows: R_res = c * τ /2 Where, τ is the transmitted pulse width and c is the velocity of light in the free space. Narrower beamwidth is very useful to distinguish two adjacent targets.

How does frequency affect radar range?

Low frequency signals have a longer wave length and will travel farther than higher frequencies. Radar transmitters with high frequency emitters are capable of measuring ranges of approximately 100 feet, which is okay for most applications.

What is the difference between range resolution and azimuth resolution of radar system?

Range (D) refers to the across-track dimension perpendicular to the flight direction, while azimuth (E) refers to the along-track dimension parallel to the flight direction. This side-looking viewing geometry is typical of imaging radar systems (airborne or spaceborne).

What is range and azimuth in radar?

Range = Distance from radar site to echo centroid. Azimuth = Horizontal angular distance from true north measured clockwise from true north. (east = 90 degrees, south = 180 degrees, west = 270 degrees, north = 0 degrees)

What is cross range resolution?

The cross-range resolution of a conventional radar is proportional to the product of the 3-dB antenna beamwidth and range. Consider a conventional imaging radar having an antenna with 2 m in length and transmitting linear FM pulses with a bandwidth of 10 MHz.