Radar detection of hazardous small scale weather disturbances

A radar method of detecting hazardous weather phenomena associated with rapidly descending events such as a downburst and which comprises the steps of:

• radiating at least one beam sufficiently large in vertical breadth to illuminate the aras encompassed by a plurality of vertically displaced receiving beams from an antenna scanned in azimuth toward a region of scatterers;
• receiving the echo powers from said plurality of beams, said echo powers being representative of the average reflectivity of the scatterers in said beams;
• determining the measure of the relationship between the echo powers between said beams at successive elevations at all range bins of a radar system, said relationship providing information representative of the vertical profile of average reflectivity of weather phenomena detected by said radar system;
• storing a sequence of said measures for successive scans of said antenna;
• determining the time difference of said measures;
• and
• generating a time history of said measures, thereby providing an early indication of rapidly changing reflectivities and profiles associated with a descending downburst and providing a changing pattern corresponding to an evolving downburst and other weather hazards.

A Doppler radar method of detecting hazardous weather phenomena comprising the steps of:

• radiating at least one beam having a predetermined vertical breadth covering an area encompassed by a plurality of vertically stacked receiving beams from an antenna scanned in azimuth toward a region of scatterers;
• receiving the echo power and corresponding reflectivities on a plurality of vertically stacked receiving beams in a predetermined number of range gates;
• measuring the components of the near surface winds along the direction of the beam from the mean Doopler velocity on one or more of the lower beams of said plurality of beams at a sequence of relatively closely spaced azimuths;
• determining the range derivative and the tangential derivative of said surface wind components from the mean Doppler velocities at successive ranges and at said closely spaced azimuths as a measure of the radial and tangential shear, respectively, associated with hazardous small scale phenomena such as downbursts or microbursts and tornadoes;
• determing the locations at which the measure of the radial and tangential shear exceed adjustable preset thresholds;
• and
• generating alarms when either of said shears exceed said thresholds.

Apparatus including a Doppler radar for detecting hazardous relatively small scale weather disturbances, comprising:

• means for radiating at least one Doppler radar beam toward a region of scatterers in an area of surveillance and scanning said beam in azimuth;
• means for receiving echo signals from said at least one Doppler radar beam in at least first and second vertically overlapping beams from said scatterers in said first and second beams from a sequence of range bins, wherein the effective differential two way beam gain of said first and second beams is of a first polarity at all angles below a predetermined null level and of a second polarity at all angles above said null level, wherein said null level corresponds to the elevation angle at which the effective two way gain of said first beam equals that of said second beam, and wherein said first and second polarities are methematically operated upon selectively to provide first and second parameters equivalent to said first and second polarities;
• means for generating the respective Doppler velocity spectra from said first and second beams from said sequence of range bins;
• means for forming a composite Doppler spectrum which is a mathematical function of the Doppler spectra of said first and second beams, said composite spectrum defining the Doppler velocity domains wherein the two Doppler spectra differ in said first and second polarity senses, one of said velocity domains including two velocity bounds in the region of said composite Doppler spectrum wherein said composite spectrum has said first polarity;
• means for detecting the first of said two velocity bounds as a measure of wind speed at said null level;
• means for detecting the second of said two velocity bounds as a measure of wind speed at a level between the height of the null level and the surface of the earth, said wind speed being defined as the radial component of the near surface wind speed;
• means for measuring the near surface wind speeds in said sequence of range bins;
• means for selectively determining a measure of the range derivative of the near surface wind speeds, the tangential derivative of the near surface wind speeds, the difference between the first and second velocity bounds, the difference between the mean reflectivities in said first and second beams, and generating output signals corresponding to said measure;
• and
• means for providing at least one indication of said output signals to thereby provide an indication of a weather disturbance in said area of surveillance, particularly the shear of the near surface winds including horizontal, vertical and tangential shear and the boundaries at which said shears exceed preset thresholds.

Apparatus including a radar system for detecting hazardous weather phenomena associated with rapidly descending events such as a downburst, comprising:

• means including an antenna scanned in azimuth toward a region of scatterers for radiating at least one beam sufficiently large in vertical breadth to illuminate an area encompassed by a plurality of vertically displaced receiving beams;
• means for receiving the echo powers from said plurality of receiving beams, said echo powers being representative of the average reflectivity of the scatterers in said beams;
• means for determining the measure of the relationship between the echo powers between said beams at successive elevations at all range bins of said radar system, said relationship providing information representative of the vertical profile of average reflectivity of weather phenomena detected by said radar system;
• means for storing a sequence of said measures for successive scans of said antenna;
• means for determining the time difference of said measures;
• and
• means for generating a time history of said measures, whereby an early indication of rapidly changing reflectivities and profiles associated with a descending downburst is provided as well as a changing pattern corresponding to an evolving downburst and other weather hazards.

Apparatus including a Doppler radar for detecting hazardous weather phenomena comprising:

• means including an antenna scanned in azimuth a region of scatterers for radiating at least one beam having a predetermined vertical breadth covering an area encompassed by a plurality of vertically stacked receiving beams;
• means for receiving the echo power and corresponding reflectivities on said plurality of vertically stacked receiving beams in a predetermined number of range bins;
• means for measuring the mean Doppler velocity and spectral width of the Doppler spectrum in each of said receiving beams and range bins;
• means for measuring the components of the near surface winds along the direction of the beam from the mean Doppler velocity on one or more of the lower receiving beams at a sequence of relatively closely spaced azimuths;
• means for determining the range derivative and the tangential derivative of said surface wind components from the mean Doppler velocities at successive ranges and at said closely spaced azimuths as a measure of the radial and tangential shear, respectively, associated with hazardous small scale phenomena such as downbursts or microbursts and tornadoes;
• means for determining the locations at which the measure of the radial and tangential shear exceed adjustable preset thresholds;
• and
• means for generating alarms when either of said shears exceed said thresholds.