Defining the Number of Samples

Defining the number of samples means balancing 2 factors: the more samples you have, the better the Doppler speed estimate and clutter filters work. However, taking many samples means you cannot move your antennas quickly.

Maximum Number of Samples

You can calculate the maximum number of samples as follows:

SAMPLES = PRF * RESOLUTION / SCAN RATE

where:

SAMPLES: Number of pulses in per ray
PRF: Number pulses you send per second
RESOLUTION: How long the sector is scanned for a single ray
SCAN RATE: Number of degrees the antenna moves per second

IRIS helps you determine the parameters in this equation, and then determines which parameter it should adjust in each case.

Number of Samples Per Ray

A ray is a collection of pulses (samples) integrated in a single data output from the signal processor.

The RVP signal processor provides several parameters to define what samples are included in a ray. The key parameters that determine the number of samples in a ray are Angle Syncing, Major Mode, and Dual PRF Velocity Unfolding.

The following table shows what constitutes a ray based on the setting of the 3 parameters. In terms of this discussion, the operation of RPHASE mode is equivalent to FFT mode

Manual tasks are always done with angle syncing off, regardless of the IRIS setting for angle syncing.

Ray Components Based on Angle Syncing, Major Mode, and Dual PRF Velocity Folding
Ray	Description
ANGLE SYNCING ON PPP MODE SINGLE or DUAL PRF	A ray of data is output by the signal processor every RESOLUTION degrees of antenna motion. Each ray consists of the integration of all pulses during the previous RESOLUTION degree of antenna motion. All radials are RESOLUTION degrees wide. The pulses selected for integration are centered on the position (`N * RESOLUTION`); where N is the number of this radial. If RESOLUTION = 1.0°, the rays are centered on integer values with ray starting and ending values on 0.5° boundaries. The setting of SAMPLES is ignored.
ANGLE SYNCING ON FFT MODE SINGLE PRF	A ray of data is output by the signal processor every RESOLUTION degrees of antenna motion. Each ray consists of SAMPLES number of pulses. This implies that the width of each radial is not necessarily equal to RESOLUTION. A ray may be wider or narrower depending on the setting of SAMPLES. The pulses selected for integration are centered on the position (`N * RESOLUTION`); where N is the number of this radial.
ANGLE SYNCING ON FFT MODE DUAL PRF	A ray of data is output by the signal processor every RESOLUTION degrees of antenna motion. The low PRF rays consist of SAMPLES number of pulses, unless there are fewer SAMPLES than pulses available during the previous RESOLUTION degrees of antenna motion. If there are fewer number of pulses available, the ray consists of the integration of all pulses during the previous RESOLUTION degrees of antenna motion. The number of pulses integrated in the PRF rays consists of SAMPLES multiplied by the DUAL PRF RATIO. This implies that the width of a ray may be narrower than RESOLUTION, but never wider. The pulses selected for integration are centered on the position (`N * RESOLUTION`); where N is the number of this radial.
ANGLE SYNCING OFF PPP MODE SINGLE or DUAL PRF	A ray of data is output by the signal processor every SAMPLES number of pulses consisting of the integration of all of these pulses. IRIS reads all rays. For manual tasks, all rays are stored. For non-manual tasks, the rays with the best angular fit are stored every RESOLUTION degrees of antenna motion. If rays are too infrequent to fit every slot in the scan, some slots have missing rays. If rays are made too frequently to fit every slot, the extra rays are discarded. In the DUAL PRF case, rays made at the low PRF are longer in time (and usually in angular distance) then the rays made at the high PRF.
ANGLE SYNCING OFF FFT MODE SINGLE PRF	A ray of data is output by the signal processor at the CPU limit of the signal processor consisting of the integration of SAMPLES number of pulses. Rays may be partially overlapping. Thus one ray may share many of the same samples with the previous ray. This sharing iterates among all rays. IRIS reads all rays. For manual tasks, all rays are stored. For non-manual tasks, the rays with the best angular fit are stored every RESOLUTION degrees of antenna motion. If rays are too infrequent to fit every slot in the scan, some slots have missing rays. If rays are made too frequently to fit every slot, the extra rays are discarded.
ANGLE SYNCING OFF FFT MODE DUAL PRF	A ray of data is output by the signal processor every SAMPLES number of pulses consisting of the integration of all of these pulses. IRIS reads all rays. For manual tasks, all rays are stored. For non–manual tasks, the rays with the best angular fit are stored every RESOLUTION degrees of antenna motion. If rays are too infrequent to fit every slot in the scan, some slots have missing rays. If rays are made too frequently to fit every slot, the extra rays are discarded. Rays made at the low PRF are longer in time (and usually in angular distance) then the rays made at the high PRF.