We briefly discuss point source and receiver technology, analyze the high density spatial sampling in situ method, introduce the symmetric sampling principles presented by Gijs J.

Method for determination of sampling frequency of routine monitoring of water quality;

Simulation of software sampling frequency adaptive algorithm for reducing spectrum leakage;

The effect of the sampling frequency on the time averaging characteristics of integrating sound level meter;

Influences of sample frequency and delays on tracking system;

The protect function can be achieved in the improvement of sample frequency.

However,the synchronous change of sample frequency and switching frequency makes the filter design complex,meanwhile the digital realization of engineering becomes difficult as the gain of controller and modulator vary with the sample frequency.

In this paper, the principle of high speed and high precision frequency sampling is presented.

In the frequency sampling method the value of transition band samples, which are usually obtained by consulting a table, must be determined in order to make the attenuation within the stopband maximal.

This paper deduces the function of stopband attenuation on the order of filter and the sampled value of transition band,according to the features of designing FIR filters with frequency sampling technique,and optimizes it with immune algorithm.