Radar apparatus

1. A radar apparatus comprising:

processing circuitry configured to

calculate a velocity of an observation target corresponding to each of a plurality of cells formed by dividing an observation area in a range direction and an azimuth direction, based on reception signals of electromagnetic waves radiated toward the observation area and reflected by the observation target in the observation area;

perform correction to remove a periodic bias component from the calculated velocity of the observation target at each cell;

determine a detection area at which there is a possibility that a detection target event occurs, based on one of relationships between a distance over the cells and a change in velocity of the observation target or between the distance over the cells, the change in velocity of the observation target, and a direction relation of velocity vectors of the observation target between the cells;

select and smooth velocities of the observation target corresponding to cells included in the detection area among the corrected velocities of the observation target, and estimate a velocity of the observation target at the detection area as a smoothed value; and

detect an occurrence of the detection target event in the detection area, based on the estimated velocity of the observation target.

2. The radar apparatus according to claim 1 , wherein the processing circuitry is configured to estimate the velocity of the observation target at the detection area as a value obtained by integrating or averaging the velocities of the observation target in a manner that depends on an observation error of the velocity of the observation target corresponding to each cell included in the detection area.

3. The radar apparatus according to claim 2 , wherein the processing circuitry is configured to perform weighted averaging of the velocities of the observation target in accordance with a standard deviation of observation errors of velocity of the observation target corresponding to each cell included in the detection area.

4. The radar apparatus according to claim 1 , wherein the processing circuitry is configured to change a size of the detection area in a manner that depends on a water depth corresponding to each cell.

5. The radar apparatus according to claim 1 , wherein the processing circuitry is configured to estimate a sea-surface velocity at the detection area as a value obtained by performing weighted averaging of sea-surface velocities in accordance with an observation error of the current velocity at a sea surface that is the observation target and a water depth corresponding to each cell included in the detection area.

6. A radar apparatus comprising:

processing circuitry configured to

calculate a velocity of a sea surface corresponding to each of a plurality of cells formed by dividing an observation area in a range direction and an azimuth direction, based on reception signals of electromagnetic waves radiated toward the observation area and reflected by the sea surface in the observation area;

perform correction to remove a periodic bias component from the calculated velocity of the sea surface at each cell;

determine a detection area including cells belonging to a wavefront candidate of a tsunami assumed in the observation area, based on a distance between the wavefront candidate of the tsunami and each cell;

smooth velocities of the sea surface corresponding to cells included in the detection area among the corrected velocities of the sea surface, and estimate a velocity of the sea surface in the detection area as a smoothed value; and

detect an occurrence of the tsunami in the detection area, based on the estimated velocity of the sea surface.

7. The radar apparatus according to claim 6 , wherein the processing circuitry is configured to perform weighted averaging of the velocities of the sea surface corresponding to the cells included in the detection area in accordance with a water depth corresponding to each cell included in the detection area, a standard deviation of observation errors of current velocity at a sea surface corresponding to each cell included in the detection area, and an angle formed by a sea surface velocity vector corresponding to each cell included in the detection area and a normal vector of the wavefront candidate of the tsunami.

8. The radar apparatus according to claim 6 , wherein the processing circuitry is configured to assume a same number of wavefront candidates of tsunami as combinations of cells about beams at both ends of a radar coverage area.

9. The radar apparatus according to claim 6 , wherein

the processing circuitry is configured to

change a detection threshold value in accordance with the number of cells included in the detection area, and

detect an occurrence of tsunami in the detection area, based on a result of comparison between the sea-surface velocity at the detection area and the detection threshold value.

10. The radar apparatus according to claim 6 , wherein

the processing circuitry is configured to

change a detection threshold value in accordance with a probability of occurrence of tsunami associated with an angle formed by a sea-surface velocity vector corresponding to each cell included in the detection area and a normal vector of the wavefront candidate of tsunami, and

detect an occurrence of the tsunami in the detection area, based on a result of comparison between the sea-surface velocity at the detection area and the detection threshold value.

11. The radar apparatus according to claim 6 , wherein the processing circuitry is configured to perform calculation of a wave height value of tsunami and prediction of arrival of tsunami, based on information about a sea-surface velocity corresponding to a cell about a beam orthogonal to a wavefront of tsunami.