CN104678078A - Soil humidity calibrating and measuring method based on global positioning system (GPS) reflected signal - Google Patents

Abstract

The invention discloses a soil humidity calibrating and measuring method based on a global positioning system (GPS) reflected signal. The method comprises seven steps: I. establishing measuring equipment for linear calibration; II. carrying out frequency conversion and noise reduction treatment on collected signals of direct-radiation and reflecting antennas by virtue of a radio frequency module and converting the signals into intermediate frequency signals; III. carrying out digital-analog conversion on the processed signals of the radio frequency module by virtue of an analog/digital (A/D) quantifying module, transmitting the signals and implementing related treatment; IV. implementing satellite pseudo random noise (PRN) extraction and storage on information of reflected signal related channels and establishing a database; V. carrying out inversion data measurement on five typical values of the reflecting antenna pointing to a soil humidity value and storing according to various satellite PRN; VI. respectively recording each satellite and corresponding soil humidity values and establishing a relation curve between corresponding reflected signal related power values and soil humidity values; and VII. carrying out linear fitting treatment by virtue of the humidity curve of the satellite PRN and the measured reflected signal power values so as to obtain a soil humidity corresponding to the reflected signal power value.

Description

A kind of soil moisture calibration measuring method based on GPS reflected signal

Technical field

The present invention relates to a kind of soil moisture calibration measuring method based on GPS reflected signal, the calibration measurements model of the reflective power value direct inversion soil moisture that the method utilizes GPS reflected signal soil humidity measurement instrument to store, belongs to and utilizes navigational satellite reflected signal inverting Detection Techniques field.

Background technology

GPS-R soil moisture retrieval is the embody rule utilizing satellite-signal to carry out earth surface remote sensing of vegetation direction, is a kind of passive type double-basis or many bases remote sensing technology.From Electromagnetic Wave Propagation basic theories angle, the characteristic information of reflecting surface is carry in this reflected signal, the change of reflected signal waveform, the change of polarization characteristic, the change of the parameters such as amplitude, phase place and frequency all directly reflects the physical characteristics of reflecting surface, directly relevant to reflecting surface in other words.For accurate estimation and the reception process of reflected signal, then can realize the estimation to reflecting surface physical characteristics and inverting, this is the theoretical foundation utilizing GPS reflected signal to carry out soil moisture retrieval.

The common method utilizing GPS-R to carry out soil moisture retrieval at present receives direct signal and reflected signal respectively by direct projection dextrorotation antenna and the left-handed antenna of reflection, and the direct signal in corresponding moment and reflection signal power value are extracted, utilize ICF model to calculate reflection coefficient, obtain soil dielectric constant and soil moisture value in conjunction with corresponding dielectric model and the relation between soil moisture and specific inductive capacity.Because dielectric model is theoretical value, utilize reflection coefficient to obtain specific inductive capacity and actual value can be variant, and do not consider the impact of the soil moisture content under different temperatures on specific inductive capacity.To calculate what utilize in soil moisture process be experimental formula utilizing in the relation between soil moisture and specific inductive capacity in addition, relation in practice then between soil moisture and specific inductive capacity and experimental formula also have very big-difference, and the existence of these factors all can have a great impact the result utilizing GPS-R to carry out soil moisture retrieval.

Summary of the invention

The object of the invention is to: a kind of soil moisture calibration measuring method based on GPS reflected signal is provided, the method raising utilizes GPS reflected signal to carry out the precision of soil moisture value and the inverting of soil moisture change trend, avoid conventional soil humidity measuring method in soil moisture retrieval process owing to utilizing theoretical formula and empirical model and obtaining in the computation process of soil moisture value dissimilar error to the impact of actual soil moisture value, this theoretical model directly uses and receives transmit signal power information by demarcating the inverting object of measurement and the soil moisture change trend that can reach soil moisture value in search coverage.

Technical scheme of the present invention is:

This measuring method mainly utilizes GPS reflection signal receiver, according to design cycle, the specific soil moisture of different direct projection antennas and reflecting antenna sensing region is carried out inverting, and the output related power result according to reflection signal receiver carries out linear calibration.

Described GPS reflection signal receiver is made up of Double RF Front End, high-speed a/d transducer, FPGA dedicated correlator, DSP, UART control interface and USB control interface etc.Relation between them is: in the sheet wherein in Double RF Front End, phaselocked loop produces 2456MHz local oscillation signal, with the signal producing 880.58MHz after the 1575.42MHz signal mixing received; The local oscillation signal mixing of this signal and 927MHz produces the analog if signal of 46.42MHz.The temperature compensating crystal oscillator of this module integration 10MHz simultaneously, for back-end digital circuit provides reference clock, its reference frequency degree of stability is ± 5 × 10-7, SMA interface is adopted to be connected with signal transacting rear end, and realize physical shielding isolation, effectively reduce the interference between frequency analog and digital circuit and noise, signal quality is further optimized.

Wherein the process data of Double RF Front End module and result are mainly carried out analog to digital conversion by high-speed a/d transducer, are calculated by the related power that digital data transmission to the FPGA module of rear end and DSP module after transforming carries out direct projection related channel program and reflected signal related channel program.

Wherein FPGA dedicated correlator major function comprises direct signal process and reflected signal process two parts, direct signal treatment channel adopt traditional advanced-instant-lag correlation channel architecture, by with DSP coordinated code and carrier track, obtain navigator fix solution.Reflected signal treatment channel carries out related operation according to the configuration information (comprising reflected signal code delay estimated value, Doppler's estimated value and corresponding control information) of DSP to reflected signal, obtain code delay-Doppler's two-dimensional complex number correlation, these complex correlation value are uploaded in host computer by USB interface.Correlation forms two-dimensional correlation performance number through 1s noncoherent accumulation simultaneously, is uploaded in host computer by UART control interface with direct signal result.

Wherein DSP mainly completes fast Acquisition and the tracking of GNSS satellite direct signal, and the information utilizing direct signal to provide solves navigator fix result, carries out pattern configurations to the processing mode of reflected signal.

Wherein in UART control interface, serial ports 1 uploads the navigation informations such as longitude, latitude and height behind location, the satellite of 12 passages number, signal to noise ratio (S/N ratio), the satellite state information such as position angle and elevation angle; Serial ports 2 uploads the related power numerical value of reflected signal related power numerical value and corresponding direct projection satellite-signal.

Wherein USB control interface realizes the digital intermediate frequency Data acquisition and storage of direct signal and reflected signal, is jointly completed by fpga chip and USB chip, and major function comprises the decoding, packing, data buffering, sequential control etc. of A/D quantized data.

Described direct projection antenna (direct projection antenna is for receiving GPS direct signal) is dextrorotation antenna, and the centre frequency of antenna is 1575.42MHz, and gain is 3dB, and standing-wave ratio (SWR) is 2:1, field angle 30 °.

Described reflecting antenna (reflecting antenna is the satellite-signal of GPS after reflecting surface scattering) is the left-handed antenna of four array high-gains, center of antenna frequency 1575.42MHz, gain 12dB, field angle 30 °.

A kind of soil moisture calibration measuring method based on GPS reflected signal of the present invention, the method concrete steps are as follows:

Step 1: the measuring equipment building linear calibration.Reception direct projection antenna is placed in antenna to add and place vertically upward, reflecting antenna is placed in 10CM place below direct projection antenna, places down with surface level is at 45 °, wherein reflecting antenna points to the reflector space that region is known soil moisture value.

Step 2: the collection signal of direct projection antenna and reflecting antenna is carried out frequency conversion and noise reduction process by radio-frequency module, transfers high-frequency signal to intermediate-freuqncy signal respectively according to direct projection passage and reflection channel.

The processing signals of radio-frequency module is carried out analog-to-digital conversion by step 3:A/D quantization modules, by the digital data transmission after conversion to FPGA dedicated correlator and DSP, at direct signal related channel program and reflected signal related channel program, relevant treatment is carried out to the digital signal after conversion respectively, obtain direct signal correlation power value and reflected signal correlation power value respectively.

Wherein direct signal correlation power value and reflected signal correlation power value are by direct signal relevant treatment passage and reflected signal relevant treatment passage, at the 1ms I that each road related channel program of direct signal and reflected signal exports, (I represents in-phase signal to Q, Q represents orthogonal signal) complex correlation value through square, add up again after summation operation, under the system in integrate-dump signal (as the 1s cycle), obtain direct signal and reflected signal two-dimensional correlation performance number.

Step 4: other information transmission of reflection signal receiver direct signal correlation power value, reflected signal correlation power value, FPGA dedicated correlator and DSP process are stored to host computer.To the information of reflected signal related channel program carry out satellite PRN extraction (satellite PRN up to standard be satellite number, to carry out reason that different satellite PRN extracts herein be different satellite varies in size reaching the signal power in measured zone), carry out corresponding reflected signal correlation power value according to different No. PRN to store, building database.

Step 5: divide according to above-mentioned steps that reflecting antenna to be pointed to soil moisture value be that five representative values such as 100,75,50,25,0 carry out invert data measurement, and store according to different satellite PRN.

Step 6: according to different satellite PRN stored data base in five representative values measured in step 5, carry out averaging operation to the storing value in reflected signal correlation power value database respectively according to the PRN of each satellite, the soil moisture value recording each satellite and correspondence respectively sets up the relation curve between corresponding reflected signal correlation power value and soil moisture value respectively.

Wherein, illustrate, if be the satellite of 1 to satellite PRN, what it was measured is the reflected signal related power of 100,75,50,25,0 for soil moisture value, and average is P100, P75, P50, P25, P0, set up five corresponding points, and matching humidity-powertrace (humidity-powertrace refers to soil moisture value and reflected signal correlation power value curve) is set up to these five points.

Step 7: the humidity-powertrace storehouse setting up each satellite PRN according to step 6, when later use reflection signal receiver carries out the inverting of soil moisture value, the reflection signal power value directly stored according to host computer calls corresponding humidity-curve library according to the satellite PRN of its correspondence, utilize the humidity-curve of respective satellite PRN and measure reflection signal power value and carry out linear fit Treatment Analysis, obtain the soil moisture corresponding to this reflection signal power value.

The invention has the advantages that:

1. this model utilize satellite reflection signal power carry out soil moisture value measure time, do not utilize theoretical model and experimental formula, avoid the error due to itself and actual value to affect the measurement of soil moisture value.

2. what this model used in two extreme values demarcation and actual soil humidity measuring of soil moisture is same set of equipment, because antenna is identical with the impact that the systematic errors such as equipment cause, therefore, utilize this programme that above-mentioned factor can be avoided the impact of soil humidity measuring.

3. this model to need in measured zone and carries out reflection signal power measurement to different satellites under meeting satellite altitude corner condition in soil moisture value calibration process, when follow-up linear measurement soil moisture, the impact of different reflection channel satellite when avoiding calculating reflection coefficient in ICF model.

4. this model is after completing the soil moisture staking-out work in measured zone, can directly utilize reflection signal power to carry out linear measurement, does not need to use direct signal information, and computation process is simple and error is less.

Accompanying drawing explanation

Fig. 1 soil moisture calibration measurements model relative humidity is the demarcation process flow diagram of 100

Fig. 2 soil moisture calibration measurements model relative humidity is the demarcation process flow diagram of 0

The actual soil humidity measuring process flow diagram of Fig. 3 soil moisture calibration measurements model

Fig. 4 soil moisture linear calibration workflow diagram

Wherein, " AD " of " in AD quantization modules " in Fig. 1 refers to " analog to digital ", and " PRN " in " PRN of satellite " refers to the numbering of satellite.Two places in Fig. 2 with Fig. 3 explain identical with Fig. 1.In Fig. 4, " humidity-powertrace storehouse " refers to soil moisture value and reflected signal correlation power value curve.

Embodiment

1. in the region needing observation and Soil Moisture, erection experimental facilities, the reflected signal soil moisture of carrying out corresponding different satellite according to the step in accompanying drawing 1 is demarcated as the work (needing the water surface be oriented to by reflecting antenna in ocean weather station observation region herein) of 100, the accompanying drawing 4 obtained by measured data analysis can illustrate and have a larger impact when reflection channel satellite changes to the power of reflected signal, the minimum value of the elevation of satellite of the receiver reflectance passage that measurement data uses is 65 degree, measure at the enterprising line time of satellite distribution figure, every gps satellite visible time is respectively 80 minutes, if there is multi-satellite elevation angle to be greater than 65 degree simultaneously, then select maximum elevation angle satellite as the power measurement object of reflection channel, then when the reflective power of receiver is measured, length has change, but impact is not had to end product.After long-time measurement, the array of the reflection signal power value corresponding to different satellite can be obtained, be respectively (i value is 1 ~ 32), respectively to obtaining array be averaged (storing frequencies that receiver receives reflection signal power is 1Hz) at corresponding time T (unit be minute), as shown in Equation 1:

$P_{r100}^i=\frac{{\mathrm{\Σ}}_1^{32}{P}_{R100}^i}{T*60}---\left(1\right)$

Obtain the reflection signal power mean value of corresponding every satellite this value is the calibration value of 100 as the relative soil moisture of the different satellite Retrieval of correspondence by (i value is the same).

2. the reflected signal soil moisture of carrying out corresponding different satellite according to the step in accompanying drawing 2 is demarcated as the work (needing the dry soil pointed to by reflecting antenna in ocean weather station observation region herein) of 0, the array of reflection signal power value corresponding to different satellite can be obtained, be designated as respectively into (i value is 1 ~ 32), respectively to obtaining array be averaged at corresponding time T (unit for minute), as shown in Equation 2:

$P_{r0}^i=\frac{{\mathrm{\Σ}}_1^{32}{P}_{R0}^i}{T*60}---\left(2\right)$

Obtain the reflection signal power mean value of corresponding every satellite this value is the calibration value of 0 as the relative soil moisture of the different satellite Retrieval of correspondence by (i value is the same).

3. be that three typical soil moisture values such as 75,50,25 are observed to soil moisture respectively according to the measuring method of step 1 and step 2, and set up the database accordingly about satellite PRN and reflection signal power value.

4. the reflection signal power Value Data storehouse of five representative values obtained according to step 1,2,3, sets up the humidity-powertrace storehouse of corresponding different satellite PRN.

5. after foundation obtains the humidity-powertrace storehouse obtained in step 4, build GPS reflected signal soil moisture sniffer, according to the workflow diagram shown in Fig. 3 and Fig. 4, by reflecting antenna towards the soil moisture region be detected, the reflected signal correlation and No. PRN, the satellite that sniffer are transferred to host computer extract, and the humidity of call establishment-powertrace storehouse is (for different satellite PRN, five the typical soil moisture values set up also have different from reflection signal power value curve), by measuring the reflection signal power value that soil obtains, fit operation is carried out with corresponding humidity-powertrace storehouse, and obtain the soil moisture value corresponding with the reflection signal power value of this measurement.

Claims (1)

1. based on a soil moisture calibration measuring method for GPS reflected signal, it is characterized in that: the method concrete steps are as follows:

Step 1: the measuring equipment building linear calibration; Reception direct projection antenna is placed in antenna to add and place vertically upward, reflecting antenna is placed in 10CM place below direct projection antenna, places down with surface level is at 45 °, wherein reflecting antenna points to the reflector space that region is known soil moisture value;

Step 2: the collection signal of direct projection antenna and reflecting antenna is carried out frequency conversion and noise reduction process by radio-frequency module, transfers high-frequency signal to intermediate-freuqncy signal respectively according to direct projection passage and reflection channel;

The processing signals of radio-frequency module is carried out analog-to-digital conversion by step 3:A/D quantization modules, by the digital data transmission after conversion to FPGA dedicated correlator and DSP, at direct signal related channel program and reflected signal related channel program, relevant treatment is carried out to the digital signal after conversion respectively, obtain direct signal correlation power value and reflected signal correlation power value respectively;

Wherein direct signal correlation power value and reflected signal correlation power value are by direct signal relevant treatment passage and reflected signal relevant treatment passage, at the 1ms I that each road related channel program of direct signal and reflected signal exports, Q, I represents in-phase signal, Q represent orthogonal signal complex correlation value through square, add up again after summation operation, under the system of integrate-dump signal, obtain direct signal and reflected signal two-dimensional correlation performance number;

Step 4: other information transmission of reflection signal receiver direct signal correlation power value, reflected signal correlation power value, FPGA dedicated correlator and DSP process are stored to host computer; Satellite PRN extraction is carried out to the information of reflected signal related channel program, carries out corresponding reflected signal correlation power value according to different No. PRN and store, building database;

Step 5: divide according to above-mentioned steps that reflecting antenna is pointed to soil moisture value is that 100,75,50,25,0 five representative values carry out invert data measurement, and store according to different satellite PRN;

Step 6: according to different satellite PRN stored data base in five representative values measured in step 5, carry out averaging operation to the storing value in reflected signal correlation power value database respectively according to the PRN of each satellite, the soil moisture value recording each satellite and correspondence respectively sets up the relation curve between corresponding reflected signal correlation power value and soil moisture value respectively;

Be the satellite of 1 to satellite PRN, what it was measured is the reflected signal related power of 100,75,50,25,0 for soil moisture value, and average is P100, P75, P50, P25, P0, set up five corresponding points, and matching humidity-powertrace is set up to these five points;

Step 7: the humidity-powertrace storehouse setting up each satellite PRN according to step 6, when later use reflection signal receiver carries out the inverting of soil moisture value, the reflection signal power value directly stored according to host computer calls corresponding humidity-curve library according to the satellite PRN of its correspondence, utilize the humidity-curve of respective satellite PRN and measure reflection signal power value and carry out linear fit Treatment Analysis, obtain the soil moisture corresponding to this reflection signal power value.