Time series signal processing

Radar time series data (also called linear "video" or I and Q) processing is done to obtain the meteorologically significant moment parameters: reflectivity, total power, velocity, width, signal quality index, clutter power correction, and optional polarization variables.

The time series are the starting point for all calculations performed in RVP10.

The time series synthesized by the FIR filter consist of an array of complex numbers:

s_{m} = [I_{m} + {j Q}_{m}] f o r m = 1, 2, 3, ..., M

where j is - 1^1/2.

Time series signal processing categories

There are two broad categories of time series signal processing:

Time Domain Processing using the I and Q samples directly to calculate "autocorrelations" and then using the autocorrelations to compute the moments.

This is used by many systems since the algorithms are very efficient requiring minimal storage and computational power. However, time domain algorithms are generally not adaptive or very flexible.
Frequency Domain Processing using the I and Q samples to calculate a Doppler power spectrum and then applying algorithms, such as clutter filtering or second trip echo filtering/extraction, in the frequency domain. The Doppler spectrum is then inverted to obtain the autocorrelation functions and these are used to calculate the moments. The frequency domain is well suited to more complex adaptive algorithms, that is, where the processing algorithm is optimized for the data.

Supported time series processing modes

RVP10 supports the following major modes, that is, processing modes to process the time series:

Supported time series processing modes
Mode	Description
DFT/FFT Mode	A frequency domain approach that is used for most operational processing applications. There are a variety of clutter filtering options, including the Gaussian Model Adaptive Processing (GMAP) algorithms.
Random Phase Mode (RPHASE)	A frequency domain approach similar to the DFT/FFT, except that filtering and extraction of both the first and second trip echoes is supported.
Pulse Pair Processing (PPP) mode	Within PPP, it is possible to first enter the frequency domain to perform spectrum based clutter filtering. The fixed and adaptive width clutter filters including the Gaussian Model Adaptive Processing (GMAP) are available with dual-polarization processing. Both of these clutter filters perform interpolation across the spectrum after ground clutter spectrum points are removed. Time domain 5-pole IIR filtering with 40 and 50 dB rejection are also available in PPP mode, but Vaisala recommends frequency-based filtering.
Batch Mode	A small batch of low PRF pulses is transmitted (for example, for 0.1° of scanning) followed by a large batch of higher PRF pulses (for example, for 0.9° of scanning) to determine which ranges are likely contaminated by second trip echo. This was developed to support a US WSR88D legacy requirement.