HF coastal current mapping radar system

• US 4,172,255 A
• Filed: 08/08/1977
• Issued: 10/23/1979
• Est. Priority Date: 08/08/1977
• Status: Expired due to Term

• Current Assignee: The United States of America as represented by the Secretary of the Interior
• Original Assignee: The United States of America as represented by the Secretary of the Interior
• Inventors: Evans, Michael W., Barrick, Donald E.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Goodwin, Lawrence
• Application Number:
  US05/822,868
• Time in Patent Office: 806 Days
• Field of Search: 73/170 A, 73/188, 73/189, 343/5 R, 343/5 W, 343/5 CE, 343/9, 343/7.7, 343/15
• US Class Current: 342/26.00D
• CPC Class Codes: G01S 13/0218 Very long range radars, e.g. surface wave radar, over-the-horizon or ionospheric propagation systems for meteorological use G01S13/95
• CPC Class Codes: G01S 13/589 measuring the velocity vector
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 13/89 for mapping or imaging
• CPC Class Codes: G01S 13/951 ground based
• CPC Class Codes: G01S 3/48 the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A system for radar remote sensing of near surface ocean currents in coastal regions. The system employs a pair of low power, transportable high frequency radar units to scatter signals from the shore off to the ocean waves. Underlying surface currents impart a slight change in velocity to the ocean waves which is detected by the radar units. Each radar unit can determine the angular direction of arrival of the radar echo signals by comparing the phase of the signals received at three short antennas on the shore. Signals scattered from the same point on the ocean by each of the two geographically separated radar units are used to construct a complete current vector for that point. The radar pair takes simultaneous measurements over an ocean area with a predetermined grid pattern. Vectors are constructed for each square section of the grid, and a map of the near surface current field is output in real-time by an on-site minicomputer.

Claims

1. A method of mapping surface current vectors in coastal waters comprising the steps of:

(a) scattering radio signals from a first radar site off waves in coastal waters to produce Doppler echos at a first radar site;

(b) sampling versus time after transmission to establish at each of different ranges from said site the Doppler echos from all directions from at least three receiving antennas to constitute a time sample;

(c) computing the range by determination of time between transmission and reception of scattered radio signals within a constant radius arc of said omni-directional sampling of step (b), corresponding to each of said time samples;

(d) measuring the coastal waters surface current components of the Doppler shift of the echos from each of the antennas in each said time sample;

(e) determining the azimuthal angles of arrival of the Doppler echos from each of the antennas in each time sample for each of said measured surface current-produced components of the Doppler shift;

(f) predetermining a plurality of map grid points to correspond to different values of range and said azimuthal angles of arrival thereat;

(g) interpolating from the values of the Doppler shift components measured in step (d) a surface current-produced component of the Doppler shift for each of said grid points;

(h) determining from the angular determinations in step (e) and said Doppler shift components found in step (g) the respective surface current vector component radial to the first radar site for each of said map grid points to constitute a first set of radial surface current vector components;

(i) repeating steps (a) through (h), contemporaneously therewith, at a second radar site to determine a second set of radial surface current vector components constituting the respective surface current vector components radial to the second radar site at each of said map grid points; and

(j) combining trigonometrically grid point correspondent radial surface current vector components of said first set and radial surface current vector components of said second set to extract thereby a complete surface current vector for each said map grid points and construct therefrom a map of the surface current field of the coastal waters.

2. The method recited in claim 1 wherein the surface current-produced components of the Doppler shift measuring step includes the steps of:

determining the total Doppler shift of the echos;

subtracting therefrom the Doppler shift due to scattering of the radio signals by gravity waves of resonant length on a stationary water surface; and

normalizing the result of the substracting step relative to the Doppler shift due to scattering of the radio signals by gravity waves of resonant length on a stationary water surface.

3. The method recited in claim 1 wherein the azimuthal angles of arrival determining step includes the step of:

measuring the phase difference between signals received by at least three spaced apart antennas at the first radar site.

4. The method recited in claim 2 wherein the surface current vector component determining step includes the step of:

multiplying the normalized result of the subtracting step by the velocity of the gravity waves of resonant length on a stationary water surface.

5. Apparatus for mapping surface current velocity vectors in coastal waters comprising a pair of pulsed radar transceivers respectively positionable at two spaced apart sites for scattering signals from said sites off waves in coastal waters to produce Doppler echos at each of said sites and sampling versus time after transmission at each of different ranges from each said site the Doppler echos from all directions, said ranges being computed in accordance with said signals times of flight, said transceivers comprising at least three spaced apart omni-directional receiving antennas at each of said two sites, means at each of said two sites for receptively connecting said antennas to a respective transceiver in time sequence during consecutive pulse transmissions and sampling from all said antennas at each range constituting a time sample, further means to measure the coastal waters surface current-produced components of the Doppler shift of the echos from each of the antennas in each said time sample, still further means to determine the azimuthal angle of arrival of the Doppler echos from each of the antennas in each time sample for each of said measured surface current-produced components of the Doppler shift, and yet still further means for determining, in accordance with said azimuthal angles and surface current-produced components, the surface current vector components radial to each of said sites and trigonometrically combining said radial components to produce realtime representations of complete surface current vectors.