CN103684464A - Under-sampling and processing method for intermediate-frequency signals of autocorrelation microwave radiometers - Google Patents

Abstract

A correlation microwave radiometer intermediate frequency signal undersampling processing method, including four steps of correlation microwave radiometer polarization signal reception, intermediate frequency IQ conversion, AD acquisition and redundant correlation, wherein the correlation microwave radiometer polarization signal reception is The radio frequency signal received by the antenna is divided into V and H polarized signals through the orthogonal mode coupler, and the intermediate frequency signal is output after low noise amplification, filtering, mixing, filtering and amplification; the received intermediate frequency signal is transmitted through the 90° power divider The signal is divided into two orthogonal 0° and 90° intermediate frequency signals, and then digital sampling is completed through AD acquisition at a sampling rate greater than 1 times the bandwidth of the received signal; redundant correlation is averaged by using two sets of redundant correlation calculation results , and finally get the complex correlation result. The invention has the advantages of reducing the sampling rate by one time under the condition of not deteriorating the complex correlation sensitivity, reducing the complexity of the system hardware caused by the high sampling rate, simplifying the signal processing algorithm and reducing the signal processing rate.

Description

A Method for Undersampling Processing of IF Signals of Correlation Microwave Radiometer

technical field

The invention relates to a method for under-sampling processing of intermediate frequency signals of a correlation microwave radiometer, which belongs to the field of microwave remote sensing.

Background technique

The simplest correlation-type microwave radiometer consists of three parts: a dual-polarized antenna system, a dual-channel superheterodyne receiver, and a digital correlator. The dual-polarized antenna system receives the microwave radiation brightness temperature from the observation scene, transforms it into mutually orthogonal polarization signals, and outputs the V-channel and H-channel signals through the orthogonal mode coupler (OMT) into the V-channel and H-channel receiving channels; The superheterodyne receiver uses a common local oscillator to down-convert the V-channel signal and the H-channel signal to an intermediate frequency, and the digital correlator first completes the AD sampling of the input signal, and then performs complex correlation processing on the four-channel signals. Correlation microwave radiometers can be used in fully polarimetric microwave radiometers and synthetic aperture microwave radiometers. A system composed of multiple correlation microwave radiometers is called a synthetic aperture microwave radiometer, and the complex correlation result output by its digital correlator is a visibility function. For a fully polarized microwave radiometer, a single correlation microwave radiometer is It can complete the extraction of full polarization information, and the complex correlation results output by its digital correlator are T3 and T4 brightness temperatures.

At present, there are mainly two methods for sampling and processing of correlation microwave radiometers: (1) After analog intermediate frequency 0° and 90° conversion, the complex correlation result is obtained through digital correlator sampling and correlation processing. For a single 0° signal and 90° ° Signal sampling is carried out according to the band-pass sampling theorem or the Nyquist sampling theorem, and its complex correlation processing adopts a non-redundant processing method. (2) Digital intermediate frequency 0°, 90° transformation, after sampling the single-channel intermediate frequency signal through a digital correlator, then perform digital 0°, 90° transformation, and then perform non-redundant complex correlation processing. This method adopts a brand-new intermediate frequency signal processing method, completes the orthogonal transformation of the intermediate frequency signal by simulating IQ, and completely restores the sampled signal through the method, and completes the correlation operation through the redundant correlation processing algorithm to finally obtain.

The shortcomings of the above method are: (1) For the analog 0°, 90° signal sampling according to the band-pass sampling theorem or the Nyquist sampling theorem, the sampling rate has not been reduced, and the sampling rate is high; 0°, 90° °The implementation form of the transformation is realized by the simulation method, which increases the hardware equipment, and increases the complexity and weight. (2) For single-channel intermediate frequency signal sampling, sampling is carried out according to the band-pass sampling theorem or the Nyquist sampling theorem, the sampling rate has not been reduced, and the sampling rate requirement is high; server resource requirements increase.

Contents of the invention

The technical solution problem of the present invention is: overcome the deficiencies in the prior art, provide a kind of correlation type microwave radiometer intermediate frequency signal processing method, under the premise of guaranteeing complex correlation sensitivity, reduce correlation type radiometer AD sampling rate, this method realizes Simple and reliable.

Technical solution of the present invention is:

A correlation type microwave radiometer intermediate frequency signal under-sampling processing method, comprising the following steps:

(1) The RF signal received by the RF antenna is divided into V and H polarized signals after passing through the orthogonal mode coupler. After the V and H polarized signals pass through the receiving channel respectively, the intermediate frequency signal is output to the 90° power splitter;

(2) Divide the intermediate frequency signal into two intermediate frequency signals of 0° and 90°: V and H signals respectively pass through a 90° power splitter to convert the intermediate frequency signal of step (1) into two orthogonal 0 of V °, 90° intermediate frequency signals and two orthogonal 0°, 90° intermediate frequency signals of the H channel, and send them to the AD acquisition chip;

(3) The AD acquisition chip samples the intermediate frequency 0° and 90° signals of the V channel and the 0° and 90° signals of the H channel at a sampling rate greater than or equal to 1 times the input signal bandwidth to obtain the V channel 0° signal, V-channel 90° signal, H-channel 0° signal, H-channel 90° signal, respectively defined as V ⁰ , V ⁹⁰ , H ⁰ and H ⁹⁰ ;

(4) Redundant processing of V ⁰ , V ⁹⁰ , H ⁰ and H ⁹⁰ in step (3): According to the formula: $\begin{array}{c}{C}_{\mathrm{Re}}={\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">V</figure-callout>}}^0\&CenterDot;h^0\\ C_{\mathrm{Im}}={\mathrm{<figure-callout\; id="90"\; label="V"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">V</figure-callout>}}^{90}\&CenterDot;h^0\\ C_{\mathrm{Re}}^R={\mathrm{<figure-callout\; id="90"\; label="V"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">V</figure-callout>}}^{90}\&CenterDot;h^{90}\\ C_{\mathrm{Im}}^R=-{\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">V</figure-callout>}}^0\&CenterDot;{\mathrm{<figure-callout\; id="90"\; label="h"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">h</figure-callout>}}^{90}\end{array}$ Perform the complex correlation operation to obtain the real part C _Re of the complex correlation result, the imaginary part C _Im of the complex correlation result, the real part C ^R _Re of the redundant complex correlation result, and the imaginary part C ^R _Im of the redundant complex correlation result, and according to the formula $\begin{array}{c}{C}_{\mathrm{Re}}^{\&prime;}=(C_{\mathrm{Re}}+C_{\mathrm{Re}}^R)/2\\ C_{\mathrm{Im}}^{\&prime;}=(C_{\mathrm{Im}}+C_{\mathrm{Im}}^R)/2\end{array}$ Get the complex correlation result of the final output.

The sampling rate required for AD sampling in the step (3) only needs to be greater than or equal to 1 times the bandwidth of the input signal, that is, the information of the V or H channel signal can be restored.

The beneficial effect of the present invention compared with prior art is:

(1) The present invention adopts the intermediate frequency 0°, 90° conversion method, and can completely restore the sampled signal when the sampling rate of AD collection is reduced by 1 time, greatly reducing the AD sampling rate and system processing rate.

(2) This method adopts a redundant correlation processing algorithm, which can improve the problem of complex correlation sensitivity reduction caused by the decrease of sampling rate, and ensure complex correlation sensitivity.

Description of drawings

Fig. 1 is a flow chart of the method of the present invention;

Figure 2 is the V (or H channel) 0°, 90° IF signal spectrum;

Figure 3 shows the sampling principle of V (or H-way) 0° and 90° intermediate frequency signals;

Figure 4 is a schematic diagram of V (or H channel) 0°, 90° IF sampling aliasing;

Figure 5 is the composite result after sampling V (or H channel) 0° and 90° intermediate frequency signals.

Detailed ways

Specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the correlation microwave radiometer consists of three parts: a dual-polarized radio frequency antenna, a receiving channel and a digital correlator. The dual-polarized antenna system receives the microwave radiation brightness temperature from the observation scene, transforms it into mutually orthogonal polarization signals, and outputs the V-channel and H-channel signals through the orthogonal mode coupler (OMT) into the V-channel and H-channel receiving channels; The receiving channel uses a common local oscillator to down-convert the V-channel signal and the H-channel signal to an intermediate frequency, and the digital correlator first completes the AD sampling of the input signal, and then performs complex correlation processing on the four-channel signals. Correlation microwave radiometers can be used in fully polarimetric microwave radiometers and synthetic aperture microwave radiometers. A system composed of multiple correlation microwave radiometers is called a synthetic aperture microwave radiometer, and the complex correlation result output by its digital correlator is a visibility function. For a fully polarized microwave radiometer, a single correlation microwave radiometer is It can complete the extraction of full polarization information, and the complex correlation results output by its digital correlator are T3 and T4 brightness temperatures.

The invention provides a method for under-sampling the intermediate frequency signal of a correlation microwave radiometer, and the specific steps are as follows:

(1) The RF signal received by the dual-polarized RF antenna passes through the orthogonal mode coupler (OMT) and is divided into V and H polarized signals, and then outputs V through the low-noise amplification, filtering, mixing, filtering, and amplification of the receiving channel. The intermediate frequency signals of the channel and channel H (the receiving channel includes low noise amplification, RF filtering, frequency mixing, intermediate frequency filtering, and intermediate frequency amplification) are output to the 90° power splitter;

(2) Divide the intermediate frequency signal into two intermediate frequency signals of 0° and 90°: V and H signals respectively pass through a 90° power splitter to convert the intermediate frequency signal of step (1) into two orthogonal 0 of V °, 90° intermediate frequency signals and two orthogonal 0°, 90° intermediate frequency signals of the H channel, and send them to the AD acquisition chip;

(3) The AD acquisition chip samples the intermediate frequency 0° and 90° signals of the V channel and the 0° and 90° signals of the H channel at a sampling rate greater than or equal to 1 times the input signal bandwidth to obtain the V channel 0° signal, V-channel 90° signal, H-channel 0° signal, H-channel 90° signal, respectively defined as V ⁰ , V ⁹⁰ , H ⁰ and H ⁹⁰ ;

As shown in Figure 2, the IF signal generation and digital sampling are completed through IF 0° and 90° sampling. The correlative microwave radiometer adds a 90° power divider at the rear end of the receiving channel, and the V and H receiving channels output 0, 90° orthogonal signals. Since the output signals are 0, 90° intermediate frequency signals, they can be equivalent to a complex Signal, since the complex signal does not have an image frequency, so it is sufficient to use fs≥B to sample the complex signal.

For the IF signal sampling of the I channel and the Q channel, according to the nature of the Fourier change, the spectrum of the I channel signal is:

X(jω)=X(-jω) (1)

The spectrum of the j*Q channel signal is:

X(jω)=-X(-jω) (2)

As shown in Figure 3, the sampling of real IF signals needs to meet the requirements of the band-pass sampling theorem, and the IF band-pass sampling of 0° and 90° signals will not alias.

As shown in Figure 4, when the band-pass sampling theorem is not satisfied, the sampling results of the 0° and 90° channels, whether it is a 0° IF signal or a 90° IF signal, are aliased.

As shown in Figure 5, after the two-way signals are synthesized, the aliased parts cancel each other out, so as long as fs≥B is satisfied, the sampling of 0° and 90° intermediate frequency signals can be completed, which is better than the minimum sampling required by the intermediate frequency sampling theorem 2 times the bandwidth of the signal is reduced by half.

(4) Perform redundant processing on V ⁰ , V ⁹⁰ , H ⁰ and H ⁹⁰ in step (3), complete the complex correlation output through redundant correlation processing, and perform complex correlation processing on the signal sampled by the digital correlator, which can The following 4 related results are obtained:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Re</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="V"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">V</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 0</span>}}\\ {\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Im</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="90"\; label="V"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">V</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 90</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 0</span>}}\\ {\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Re</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="90"\; label="V"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">V</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 90</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 90</span>}}\\ {\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Im</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="V"\; filenames="HDA0000426524890000011.png"\; state="\{\{state\}\}">V</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 90</span>}}\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, C _Re = C ^R _Re , C _Im = C ^R _Im , C _Re is the real part of the cross-correlation, C _Im is the imaginary part of the cross-correlation, C ^R _Re is the real part of the redundant cross-correlation, and C ^R _Im is the redundant Cross-correlation imaginary part.

Generally, correlation microwave radiometers only need to obtain _{C Re} and C _Im to obtain the real and imaginary parts of _the complex correlation _. However, due to the use of intermediate frequency signal processing methods, ^it is necessary _to obtain ^all information, its complex correlation real part and imaginary part are:

$\begin{array}{c}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Re</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Re</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Re</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}}\\ {\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Im</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Im</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; Im</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}}\end{array}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

倍，γ为实际采样率与带通采样率的比值。This can ensure that its complex correlation sensitivity is the same as the complex correlation sensitivity obtained by using the band-pass sampling theorem, otherwise its sensitivity is reduced

times, γ is the ratio of the actual sampling rate to the bandpass sampling rate.

Sampling and analysis of the intermediate frequency signal of a meteorological satellite, the center frequency of the intermediate frequency of the noise is f0=1.2GHz, and the bandwidth is B=1.5GHz. The sampling frequencies of 4G, 2G and 1G are respectively used for sampling. The analysis results are shown in Table 1

Table 1 Analysis of test results of a meteorological satellite

It can be seen from the above table that when the sampling frequency is 4G (satisfies the sampling theorem) and 2G, the results after redundant processing are basically the same in accuracy. From this we can see that when the sampling rate of AD collection is reduced by 1 times, it can be completely The recovered sampled signal further illustrates the correctness of the method of the present invention.

The contents not described in detail in the description of the present invention belong to the well-known technology of those skilled in the art.

Claims (2)

1. a correlation type microwave radiometer intermediate frequency signal undersampling processing method, it is characterized in that the steps are as follows: (1) The RF signal received by the RF antenna is divided into V and H polarized signals after passing through the orthogonal mode coupler. After the V and H polarized signals pass through the receiving channel respectively, the intermediate frequency signal is output to the 90° power splitter; (2) Divide the intermediate frequency signal into two intermediate frequency signals of 0° and 90°: V and H signals respectively pass through a 90° power splitter to convert the intermediate frequency signal of step (1) into two orthogonal 0 of V °, 90° intermediate frequency signals and two orthogonal 0°, 90° intermediate frequency signals of the H channel, and send them to the AD acquisition chip; (3) The AD acquisition chip samples the intermediate frequency 0° and 90° signals of the V channel and the 0° and 90° signals of the H channel at a sampling rate greater than or equal to 1 times the input signal bandwidth to obtain the V channel 0° signal, V-channel 90° signal, H-channel 0° signal, H-channel 90° signal, respectively defined as V ⁰ , V ⁹⁰ , H ⁰ and H ⁹⁰ ; (4) Redundant processing of V ⁰ , V ⁹⁰ , H ⁰ and H ⁹⁰ in step (3): According to the formula: $\begin{array}{c}{C}_{\mathrm{Re}}=V^0\&Center\; Dot;h^0\\ C_{\mathrm{Im}}=V^{90}\&Center\; Dot;h^0\\ C_{\mathrm{Re}}^R=V^{90}\&CenterDot;h^{90}\\ C_{\mathrm{Im}}^R=-V^0\&CenterDot;h^{90}\end{array}$ Perform the complex correlation operation to obtain the real part C _Re of the complex correlation result, the imaginary part C _Im of the complex correlation result, the real part C ^R _Re of the redundant complex correlation result, and the imaginary part C ^R _Im of the redundant complex correlation result, and according to the formula $\begin{array}{c}{C}_{\mathrm{Re}}^{\&prime;}=(C_{\mathrm{Re}}+C_{\mathrm{Re}}^R)/2\\ C_{\mathrm{Im}}^{\&prime;}=(C_{\mathrm{Im}}+C_{\mathrm{Im}}^R)/2\end{array}$ Get the complex correlation result of the final output. 2. A method for undersampling the intermediate frequency signal of a correlation microwave radiometer according to claim 1, characterized in that: the sampling rate required for AD sampling in the step (3) only needs to be greater than or equal to 1 times The bandwidth of the input signal is carried out, that is, the information of the V or H channel signal can be restored.

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