CN1306276C - Post processing method for observing data of drop-down acoustic Doppler current profile instrument - Google Patents

Abstract

Post-processing method for observation data of drop-in acoustic Doppler current profiler. Firstly, the raw data of LADCP, CTD and GPS are initially processed to realize their synchronous fusion; then all the observations of LADCP are converted into the vertical shear velocity of each adjacent observed water layer; then the "bottom tracking method" is used to obtain Take the absolute flow velocity profile from the surface to the bottom in the observed water column; then use the "GPS method" to obtain the absolute flow velocity profile from the bottom to the surface in the observed water column; finally, couple the two types of absolute flow velocity profiles obtained above into the entire observation Absolute velocity profile of ocean current motion in the water column. The present invention is characterized in that the absolute velocity profile of ocean current movement can be obtained according to LADCP, CTD and GPS raw data obtained by on-site synchronous observation. It is expected that a large amount of data observed by my country's launch-type acoustic Doppler current profiler can be fully utilized.

Description

Post-processing method of observation data of drop-in acoustic Doppler current profiler

technical field

Post-processing method of observation data of Lowered Acoustic Doppler Current Profiler (LADCP).

Background technique

LADCP is a new observation instrument emerging in the field of international ocean current monitoring technology in recent years, and it has also been introduced by major domestic oceanographic institutions. However, the manufacturer of LADCP can only provide the relevant pre-processing software (which can only realize the transformation of the acoustic signal), but is powerless to post-process the data. The current basic situation is as follows:

1) The observation purpose of the LADCP instrument is to obtain the absolute velocity profile of the ocean current movement, but its observation feature is to realize the measurement of the ocean current vector during the movement process, and the movement velocity of the LADCP instrument itself is generally relatively large ( It is the same order of magnitude or one order of magnitude larger than the movement velocity of the observed water body), so the direct observation result of LADCP can only be the velocity of the ocean current relative to the moving instrument. For the post-processing of LADCP data, the most direct idea is to first measure the velocity of the LADCP instrument itself. However, under the current technical conditions, it is still difficult to measure the velocity of the underwater LADCP instrument with high precision. Therefore, the first question arises: how to obtain the absolute velocity profile of the ocean current movement under the condition that the velocity of the LADCP instrument itself is unknown?

2) Multi-instrument synchronous observation has become a popular trend in the field of marine surveys. Based on this consideration, the LADCP instrument does not carry pressure, conductance and other sensors in its innate hardware design, so that it cannot determine the different observation times during the observation process. Therefore, LADCP observation is actually a complete LADCP observation system composed of LADCP, Conductivity-Temperature-Depth System (CTD) and Global Position System (GPS). Therefore, the second question arises: how to realize the reasonable fusion of LADCP, CTD and GPS observation data?

The solution to the above problems not only involves the technical problems of the LADCP instrument itself, but also involves the ocean current movement in the physical oceanography research, and is closely related to the actual realization of the marine field survey, which is the key to the post-processing of the LADCP data. Due to the difficulty of solving it, a large amount of LADCP observation data cannot be processed objectively and effectively, resulting in a great waste of resources.

Contents of the invention

The purpose of the present invention is to provide an objective and effective LADCP data post-processing method, to realize the LADCP, CTD and GPS raw data obtained by synchronous observation on the spot, and obtain the absolute velocity profile of the ocean current movement under the condition of unknown LADCP instrument own movement velocity , so that a large amount of measured data obtained from LADCP observations can be fully utilized.

The present invention firstly carries out preliminary processing to the raw data of LADCP, CTD and GPS, realizes the synchronous fusion of three kinds of data; The difference is equal to the difference of absolute velocity", transform all the observed values of LADCP into the vertical shear flow velocity of each adjacent observed water layer; then use the "bottom tracking method" to obtain the absolute flow velocity from the surface to the bottom in the observed water column Then the absolute flow velocity profile from the bottom to the surface in the observed water column is obtained by the "GPS method"; finally, the two types of absolute flow velocity profiles obtained above are synthesized through weight coupling, and the absolute velocity of the ocean current movement of the entire observed water column is obtained profile.

Description of drawings

Schematic diagram of LADCP tiled data in Fig. 1 in the present invention

(where each vertical line represents a velocity profile measured by LADCP)

The specific implementation flowchart of Fig. 2 the present invention

Detailed ways

The specific implementation flow chart of the present invention is shown in Fig. 2 .

1. Data initial processing, including LADCP data initial processing, CTD data initial processing and GPS data initial processing, and realize their synchronous fusion. The specific steps are as follows:

a. LADCP data initial processing: Use the LADCP data initial processing software of BBLIST1.0 or above version provided by the instrument manufacturer to convert the acoustic signal of the observation data and process it into one section per second (all the results of each LADCP observation called a profile) time series data.

b. Preliminary processing of CTD data: Use the software provided by the instrument manufacturer (each CTD has its own matching data processing software) for initial data processing, and process it into 1 data per second (combine all the results of each CTD observation is called a sample, and the average result of several samples is called a time series data).

c. Preliminary processing of GPS data: Extract the positioning information synchronized with the LADCP/CTD observation process from the GPS observation data, and process it into 1 data per second (all the results received by GPS at each moment are called a sample, several The average result of the sample is called a data) time series data.

d. Synchronous fusion of three kinds of data: Since the observation process of LADCP and CTD is carried out synchronously, their exit and entry points are the same. Go to the LADCP time series data of 1 second profile.

2. Convert all observed values of LADCP into vertical shear velocity of each adjacent observed water layer

a. The characteristics of LADCP "tile data": if the observation effect of the Acoustic Doppler Current Profiler (ADCP) is regarded as the effect of a string of current meters, then the actual observation of LADCP is like dragging the string of current meters Doing lowering and rising movements. If one LADCP observation is called a section, and all the observation data of any water layer in each section is called a data, then there will be a continuation of sections and interlacing of data and data in the observation results of LADCP, especially It is a succession of velocity profiles, just like the superposition of roof tiles, so it is called "tile data" (Figure 1).

b.Characteristics of LADCP observation data: based on "tile data", it can be found that the measurement process of each section of LADCP is very short (usually 0.1s-0.3s), so that the velocity change of the instrument itself during this period It is very small, so that the movement speed of the LADCP instrument during this period can be regarded as a constant. Therefore, in any same section observed by LADCP, the velocity relationship of each observed water layer can be expressed as follows:

Va1＝VL+V1

Va2＝VL+V2

Va3＝VL+V3

Va4＝VL+V4

                        ...

Among them: Va1, Va2, etc. are the absolute speeds of each water layer, VL is the moving speed of the LADCP instrument itself, V1, V2, etc. are the measured values of each water layer LADCP, then:

Va1-Va2＝V1-V2

Va2-Va3＝V2-V3

Va3-Va4＝V3-V4

                        ...

It can be seen from these formulas that "the difference between the measured LADCP values of two adjacent water layers in the same section is equal to the difference in the absolute velocities of the two water layers". This is the most basic characteristic of LADCP observation data, and also the most critical basis for the realization of this step. In this way, although the direct measurement value of LADCP cannot reflect the objective properties of ocean current movement, the difference between the measured values of two adjacent water layers in the same section is a true reflection of the characteristics of ocean current movement.

c. According to the above, convert all the observed values of LADCP into the vertical shear velocity of each adjacent observed water layer: for each section observed by LADCP, subtract the measured values of LADCP of each adjacent water layer , to get the velocity shear variable between them, and then divided by the layer thickness to get the corresponding shear rate. In this way, several shear rate values are obtained for each water layer in the observed water column. It is worth pointing out that since the vertical velocity of seawater is generally very small, it is almost difficult to distinguish it by the measurement method of LADCP. Therefore, the velocity mentioned in this specification refers to the horizontal velocity of seawater, and the shear rate refers to the horizontal velocity. Velocity vertical shear rate.

3. The "bottom tracking method" obtains the absolute flow velocity profile from the bottom to the surface in the water column. The specific steps are as follows:

a. Extract data with bottom tracking information from the fused LADCP data sequence;

b. Select the near bottom layer as the reference layer, and obtain the relative flow velocity of each water layer in the observed water column relative to it: first, conduct a Gaussian distribution test on all shear rate values of each water layer, and then perform a confidence interval with a confidence degree of 0.95 Carry out the arithmetic average or other statistical average of the data to obtain the flow velocity shear rate of the water layer; proceed accordingly to obtain the flow velocity shear rate of all water layers; starting from the reference layer, the shear rate value is calculated according to the The depth recursive integration is carried out in the sequence to the surface layer to obtain the relative flow velocity of each water layer relative to the reference layer;

c. Obtain the absolute velocity of the near-bottom reference layer based on the bottom tracking information data: the bottom tracking information of LADCP (can only be obtained near the bottom layer) refers to the velocity V _{bottom tracking} of the seabed relative to the LADCP instrument obtained by LADCP observation, and For the geodetic coordinate system, the seabed is stationary, so the reverse value of this kind of observation value is actually the velocity V _measurement of the LADCP instrument’s own movement, and the reference layer can be obtained by directly interacting with the LADCP measurement value The absolute velocity V of _{the reference layer} :

V _{reference layer} = V _test - V _{bottom tracking} (1)

d. Obtain the absolute flow velocity profile from the bottom to the surface in the observed water column: the absolute flow velocity of the reference layer and the relative flow velocity of each water layer relative to the reference layer have been obtained above, and the absolute flow velocity profile of the entire water column only needs to be calculated for each The water layer applies the following simple formula:

Vn _-absolute = _Vref + Vn _{-relative to the reference layer} (2)

where n represents each water layer in the observed water column.

4. The "GPS method" obtains the absolute flow velocity profile from the surface to the bottom in the water column. The specific steps are as follows:

a. Extract data with GPS information from the fused LADCP data sequence;

b. Select the near-surface layer as the reference layer, and obtain the relative flow velocity of each water layer in the observed water column relative to it: first, conduct a Gaussian distribution test on all shear rate values of each water layer, and then perform a confidence interval with a confidence degree of 0.95 Carry out the arithmetic average or other statistical average of the data to obtain the flow velocity shear rate of the water layer; proceed accordingly to obtain the flow velocity shear rate of all water layers; starting from the reference layer, the shear rate value is calculated according to the Depth recursive integration is carried out in the order to the bottom layer to obtain the relative flow velocity of each water layer relative to the reference layer;

c. Calculating the absolute flow velocity of the near-surface reference layer based on GPS information: In terms of the utilization of GPS information, the most direct idea is to directly apply the GPS positioning information to the velocity determination of the LADCP instrument itself. However, not only the positioning accuracy of GPS cannot meet the requirements of this use, but also there is a very significant relative motion between the LADCP instrument itself and the GPS antenna, so the positioning information of GPS cannot be directly applied to the determination of the speed of the LADCP instrument itself . However, in the measurement process of LADCP, it is always possible to make the LADCP enter the water from a certain position of the survey ship, and then exit the water from the same position, that is, "the relative position of the LADCP and the survey ship remains the same when entering the water and when exiting the water. changing". Therefore, during the whole measurement process, the time integral of the velocity V _LADCP of the LADCP instrument itself is equal to the horizontal displacement of the measuring ship, and its formula is expressed as follows:

$\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; T</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; LADCP</span>}}\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; ship</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; ship</span>}}^{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; DX</span>}}_{\mathrm{<span\; class="notranslate">\; ship</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, X _ship ^T refers to the position of the survey ship at the water point, X _ship ⁰ refers to the position of the survey ship at the water entry point, and DX _ship refers to the horizontal displacement of the survey ship during the entire measurement process.

Taking this as the basis for the design of this part, the specific steps to obtain the near-surface reference absolute velocity profile using GPS information are as follows:

i. First, the absolute velocity _Vabsolute for any specific water layer can be characterized by the sum of the velocity _VLADCP of the LADCP instrument itself and _{the measured} value V of the LADCP:

V _absolute = V _LADCP + V _measured (4)

It can also be characterized by the sum of the reference layer velocity V _absolute and relative to the reference layer velocity V _{relative to the reference layer} :

V _absolute = V _{reference layer} + V _{relative to reference layer} (5)

So you can get:

V _{reference layer} = V _LADCP + V _measured - V _{relative to reference layer} (6)

ii. Integrate the above formula over the time interval T of the entire measurement process, and combine with (3) formula,

Available:

The first item on the right side of the above formula is determined by GPS information, and the second and third items are directly obtained from the measured value of LADCP and the aforementioned processing steps. In this way, when the GPS positioning information cannot be directly used to determine the speed of the LADCP instrument itself, considering the entire measurement process, using the invariance of the relative position of the LADCP when it enters the water and when it exits the water, the near-surface reference layer is obtained. speed.

d. Obtain the absolute flow velocity profile from the surface to the bottom in the observed water column: combine the absolute flow velocity of the reference layer obtained above with the relative flow velocity of each water layer relative to the reference layer to obtain the flow velocity of each water layer in the entire water column Absolute flow rate, its formula is expressed as:

Vn _-absolute = _Vref + Vn _{-relative to the reference layer} (8)

where n represents each water layer in the observed water column.

5. Obtain the absolute velocity profile of the ocean current movement of the entire observed water column through weight coupling: Whether it is the "bottom tracking method" or the "GPS method", in the process of obtaining the absolute velocity profile of the observed water column ocean current movement, the corresponding integral is involved In this way, with the prolongation of the integration process, the cumulative effect of measurement error will inevitably be caused. However, the "bottom tracking method" integrates from the bottom layer to the surface layer, and the error accumulation increases upward; the "GPS method" integrates from the surface layer to the bottom layer, and the error accumulation increases downward. Therefore, according to the reverse order of their error accumulation, the corresponding coupling processing can be performed to realize the process control with smaller errors. The specific steps are as follows:

a. The absolute velocity profile of the entire observed water column obtained by the "bottom tracking method" is called the "bottom tracking profile"; the absolute velocity profile of the entire observed water column obtained by the "GPS method" is called the "GPS profile ”; to unify the format of them, that is to realize the unification of the position of the data points of each water layer, and the unification of the interval and length of the entire data sequence.

b. Coupling of "reference data segment": compare and analyze the "bottom tracking profile" and "GPS profile", and obtain the data segment (generally located in the middle segment) with the closest speed between them, which is called "reference data segment". The respective weights in the coupling of this section of data are taken as 50%, and the absolute flow velocity of each water layer in this section is synthesized.

c. Coupling from the "reference data section" down to the bottom layer: determine the weight coefficient of each water layer from the "baseline data section" down to the bottom layer from the "baseline data section" to linearly increase from 50% to 100%; determine The weight coefficient of each water layer in the "GPS profile" from the "reference data section" down to the bottom layer decreases linearly from 50% to 0%; then each water layer is synthesized separately to obtain the absolute flow velocity of each water layer in this section.

d. Coupling from the "reference data segment" up to the near-surface layer: determine the weight coefficient of each water layer from the "base-tracking section" up to the near-surface layer from 50% to 0% linearly; determine The weight coefficient of each water layer in the "GPS profile" from the "reference data section" to the near surface layer increases linearly from 50% to 100%; then each water layer is synthesized separately to obtain the absolute flow velocity of each water layer in this section.

In summary, the present invention thus constructed can obtain the absolute velocity profile of ocean current movement under the condition that the velocity of the LADCP instrument itself is unknown based on the LADCP, CTD, and GPS raw data obtained from on-site synchronous observations. It is expected that a large amount of data observed by my country's launch-type acoustic Doppler current profiler can be fully utilized.

Claims (2)

1. the post-processing approach of observing data of drop-down acoustic Doppler current profile instrument is characterized in that at first the source book of LADCP, CTD and GPS is carried out just handling, and realizes that the synchronism of three kinds of data merges; Then, all observed readings of LADCP are converted into the vertical shear flow velocity of each adjacent observation water layer in view of " watt repeatedly formula data " characteristics of LADCP and the characteristic of " difference with the measured value of adjacent two water layers in the section equals the poor of absolute velocity "; Ask for the interior absolute fluid velocity profile of observation water column by " end tracing " then by the table and the end; Ask for the interior absolute fluid velocity profile of observation water column by " GPS method " again by the end and table; At last, the absolute fluid velocity profile of two classes of above-mentioned gained is synthesized by weight, just obtained the ocean current motion absolute velocity section of whole observation water column, the step of the above-mentioned ocean current motion absolute velocity section that passes through the whole observation water column of weight coupling acquisition is:

A. the ocean current motion absolute velocity section of the whole observation water column that is obtained by " end tracing " is called " end tracking section "; The ocean current motion absolute velocity section of the whole observation water column that is obtained by " GPS method " is called " GPS section "; They are carried out the uniform format processing, realize that promptly the material point position of each water layer is unified mutually, the interval of whole data sequences is unified mutually with length;

B. the coupling of " benchmark data section ": comparative analysis " end tracking section " and " GPS section ", ask for the most approaching data section of speed between them, be called " benchmark data section ", during this section data is coupled separately weight all be taken as 50%, the synthetic absolute flow velocity that obtains each water layer of this section;

C. from " benchmark data section " down up to the coupling of near-bottom: determine " end tracking section " from " benchmark data section " down up to the weight coefficient of each water layer of near-bottom from 50% linear increment to 100%; Determine " GPS section " from " benchmark data section " down up to the weight coefficient of each water layer of near-bottom from 50% linear decrease to 0%; Each water layer is synthetic respectively then, obtains the absolute flow velocity of each water layer of this section;

D. from " benchmark data section " up up to the coupling on nearly top layer: determine " end tracking section " from " benchmark data section " up up to the weight coefficient of each water layer on nearly top layer from 50% linear decrease to 0%; Determine " GPS section " from " benchmark data section " up up to the weight coefficient of each water layer on nearly top layer from 50% linear increment to 100%; Each water layer is synthetic respectively then, obtains the absolute flow velocity of each water layer of this section.

2. the post-processing approach of observational data as claimed in claim 1, it is characterized in that it is at first all shear rate values of each water layer to be carried out the Gaussian distribution check with respect to the step of the relative velocity of reference layer that interior each water layer of water column is observed in above-mentioned asking for, be that 0.95 fiducial interval is carried out data arithmetic mean or other statistical average to degree of confidence then, thereby try to achieve the flow velocity shear rate of this water layer; Continue according to this, obtain the flow velocity degree shear rate of all water layers; From reference layer, the shear rate value is carried out degree of depth stepping type integration according to the order from the bottom to the top layer, obtain the relative velocity of each water layer with respect to reference layer.

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