RU2500985C1 - Method for remote detection of subsidence, thickness and height of ice - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: in the method properties of a sonar interferometer are used, which is realised in the form of a sideward-looking interferometric sonar, they measure in a wide swath the heights of z_i points of the lower ice surface relative to the horizontal plane stretching via the middle point of the interferometer base, and also horizontal distances L_i from the middle point of the interferometer base to these points of the lower ice surface, with subsequent calculations of ice thickness H_i according to the values of its subsidence d_i with the help of the equation of linear regression of type H_i (cm) = ad_i (cm) + b (cm), making it possible to take into account seasonal changes of floating ice density and height of snow cover on it, which substantially increases accuracy of ice thickness measurement in comparison with the prototype. At the same time the height of ice e_i may be calculated in accordance with the formula e_i=(H_i-d_i). The width of the swath L_i of the non-ridged ice, in which it is possible to measure subsidence, thickness and height of ice by the proposed method, makes L_i=(4-5)h₀.

EFFECT: determination of morphometric characteristics of floating ice cover along the area of the ice surface with high accuracy specified by elimination of errors in estimation of ice thickness arising as a result of seasonal changes of floating ice density and height of snow cover on it.

3 cl, 2 dwg

Description

The invention relates to the field of hydroacoustics and is intended for remote acoustic measurements of the morphometric characteristics of floating ice from under water.

The main morphometric characteristics of floating ice include: sediment, ice thickness and height, as well as the relief profile of the lower and upper surfaces of the ice cover [1].

Known methods for remote determination of precipitation and thickness of ice, as well as building a profile of the relief of its lower surface using hydroacoustic means, which are described, for example, in [2, p.133-158.].

The main disadvantages of the known methods for remote determination of precipitation and ice thickness using sonar is:

The impossibility of determining the precipitation, thickness and height of the ice sheet in the field of view above the sonar carrier and, as a consequence, their low productivity in the study of the ice sheet. This disadvantage is due to the fact that the known methods, in principle, make it possible to evaluate the morphometric characteristics of the ice cover in its section by a vertical plane (profile measurements), and not by its area [2].

The low accuracy of measuring the thickness H _{i of the} floating ice sheet, as well as the impossibility of measuring its height above the water surface and constructing the profile of the upper surface of the ice sheet. Errors in estimating the thickness of ice arise because the method does not take into account the height of the ice above the surface of the water, which depends on the density of floating ice and the height of the snow cover on it, having pronounced seasonal changes.

The closest analogue of the proposed method, selected as a prototype, is the method described in [2, p.133-135]. This method of determining precipitation and ice thickness from an underwater object (submarine, submarine, submerged buoy station) is characterized by the following operations:

- radiation in the direction of the surface of the reservoir using a pulsed sonar, which uses an echo sounder, sounding signals and the subsequent reception of acoustic echo signals reflected (scattered) by the water / ice interface;

(i=1, 2, …n) между точкой отражения и горизонтальной плоскостью, в которой находится антенна эхолота;- calculation of the delay time of the echo of the shortest distance $$r_{A_i}$$

(i = 1, 2, ... n) between the reflection point and the horizontal plane in which the sonar antenna is located;

антенны эхолота;- simultaneous measurement of the immersion depth with a hydrostat $$h_{A_i}$$

depth sounder antennas;

между глубиной погружения антенны эхолота и кратчайшим расстоянием между точкой отражения (рассеяния) акустического эхо-сигнала и горизонтальной плоскостью, в которой находится антенна эхолота;- calculation of ice precipitation d _i at the reflection point of the sounding acoustic signal, as the difference $$d_i=h_{A_i}-r_{A_i}$$

between the immersion depth of the echo sounder antenna and the shortest distance between the reflection point (scattering) of the acoustic echo signal and the horizontal plane in which the echo sounder antenna is located;

- building a profile (section) of the lower boundary of the ice sheet using successive values of ice precipitation d _i when moving the sonar.

Ice precipitation values d _i obtained in this way are often used as actual values of the floating ice thickness H _i . However, practice shows that such an approximation in estimating ice thickness can cause errors of up to 20% or more of the measured ice thickness, which makes it incorrect to compare the results of these measurements with data obtained by other measuring devices.

The disadvantage of this method is the lack of operations in it, allowing for one cycle "radiation - reception" to determine the draft, thickness and height of floating ice in the field of view above the underwater object, and also take into account errors in estimating the thickness of the ice arising from seasonal changes in the density of floating ice and snow depth on it. In addition, according to the results of one “radiation-reception” cycle, data on the draft and thickness of ice can be obtained only at one point on its surface located above the sounder antenna.

The technical result of the invention is the ability to measure the morphometric characteristics (precipitation, thickness and height) of floating ice from under water in a wide field of view with increased accuracy.

,To achieve the specified technical result, a method for determining precipitation and ice thickness from an underwater object, including emitting a sonar emitting antenna from an underwater object in the direction of the surface of the reservoir of sounding signals, receiving acoustic echo signals reflected by the water / ice interface and simultaneously measuring absolute hydrostatic pressure using a hydrostat p new signs have been introduced on the sonar, namely, an interferometer is used as a sonar, the receiving antennas of which I have directivity characteristics (XI) narrow in horizontal and wide in vertical planes and spaced vertically by a distance D, which is the base of the interferometer, receive the echo signals by both receiving antennas in the range of angles Θ covered by their CN, and measure the distance between the zero line corresponding to the interference pattern the middle of the interferometer base and the middle of the interference band corresponding to the reflection points from the lower ice surface of the received echo signals, proportional to the distance of these points of reflection ity due to the middle of the interferometer base, using a scale bar, determining the slope distances r _i points reflection echo signal to the middle of the interferometer base, indicated at 1a point 0, the formula $$z_i=r_i\frac{i{\lambda }_0}{D}$$

,

where i = 1, 2, 3 ... n is the number of the interference band counted from the zero line on the interference pattern corresponding to the moment of radiation of the probe signal, λ ₀ is the wavelength of the received echo signal, determine the height z _{i of} each i-th reflection point from the lower surface of the ice relative to the horizontal plane passing the middle of the base of the interferometer, according to the formula $$L_i=r_i\sqrt{\mathrm{one}-{\left(\frac{i{\lambda }_0}{D}\right)}^2}$$

determine the horizontal distance L _i from the middle of the base of the interferometer 0 to each i-th reflection point, using the values of height z _i calculate ice precipitation d _i at each i-th reflection point from the bottom surface of the ice and at the corresponding horizontal distance L _i using the formula d _i = h ₀ -z _i , where h ₀ is the depth of the middle of the base of the interferometer relative to the surface of the water, calculated by the formula h ₀ = (pp _atm ) k ₁ k ₂ , where p _atm is the atmospheric pressure above the ice surface at the location of the object, k ₁ , correction for the vertical average density of sea water ρ and k ₂ are gravity corrections, respectively, the ice thickness H _{i is} calculated using the linear regression equation of the form H _i (cm) = a d _i (cm) + b (cm), where a and b are empirical regression coefficients taking into account seasonal changes in the density of floating ice and the height of the snow cover on it, for each of the three main seasons of the annual cycle, at each i-th point, the height of the floating ice e _i relative to the surface of the water is calculated as the difference in the values of its thickness and precipitation at surface points using the formula e _i = (H _i -d _i ) and from the obtained L _i , d _i and e _i build the profiles, respectively, of the lower and upper surface of the voiced section of floating ice in the field of view corresponding to the range of angles covered by the directivity characteristics of the interferometer.

The best result is obtained if the emitting antenna is located at the midpoint of the base of the interferometer.

The empirical regression coefficients can be determined for the summer season (June 16 - September) a = 0.83, b = 39.2, for the autumn season (October-November) a = 1.084, b = 0.6 and the winter season (December - June 15) a = 1,070, b = 4,6,

The root-mean-square error of calculating the ice thickness according to the equation H _i (cm) = a d _i (cm) + b (cm) for the winter period does not exceed 3 cm with an ice thickness of 350 cm (relative error 0.85%). In the autumn and summer periods, the value of the correlation coefficient between the thickness and ice sediment decreases to 0.91, and the standard error increases to 4-5 cm [3]. These measurement errors are significantly less than that of the prototype.

The essence of the method is illustrated in figure 1 and figure 2.

On figa is a diagram explaining the method, where in a projection on a vertical plane shows:

A ₁ , A ₂ - receiving acoustic antennas of the interferometer;

D is the base of the interferometer;

0 - midpoint of the base of the interferometer;

l is the geometric difference in the echo path from a point on the ice surface M to the antennas of the interferometer;

r _i is the slant range from the base of the interferometer to the point on the ice surface;

z _i - the height of the point on the surface of the ice relative to the horizontal plane passing through the midpoint of the base of the interferometer;

h ₀ - the depth of the midpoint of the base of the interferometer relative to the surface of the water;

Θ is the angle measured from the axis of the XN antenna in the vertical plane;

θ _i is the slip angle;

L _i is the horizontal distance from the midpoint of the base of the interferometer to a certain point on the ice surface;

d _i - ice sediment;

H _i is the thickness of the ice;

e _i is the height of the ice.

On figb presents a structural diagram that implements the proposed method. The block diagram contains: a radiating antenna of the interferometer A, receiving acoustic antennas of the interferometer A ₁ , A ₂ ; 1 - generator device, 2 - receiving amplifiers, 3 - phase discriminator, 4 - recorder (indicator), 5 - device for determining the number i of the interference band, 6 - calculator of the angle of slip θ _i , 7 - calculator of height z _i and horizontal range L _i , 8 - device for calculating ice precipitation d _i , 9 - device for calculating ice thickness H _i , 10 - device for calculating ice height e _i , 11 - interferometer known from [4].

Figure 2 presents a view of the interference pattern at the output of the interferometer, where 1 is the zero line (the origin of the oblique range), corresponding to the moment the interferometer emits the probe signal, x ₁ is the distance from the zero line to the first interference band corresponding to the oblique range of r ₁ to the point ice surface.

The method is characterized by the following operations:

At some point in time, the radiating antenna of the interferometer emits an acoustic pulse sounding radio signal to the side of the water surface. Since the axes of the directivity characteristics (CH) of the interferometer antennas in the horizontal plane are perpendicular to the diametrical plane of its carrier, the lower surface of the ice is irradiated with acoustic energy in the direction perpendicular to the carrier line. Due to the narrow in the horizontal and wide in vertical planes XI emitting antenna of the interferometer, a narrow in the horizontal and wide in vertical planes strip of the lower surface of the ice is irradiated.

After the probe signal is emitted, the interferometer switches to the mode of receiving echo signals scattered by the lower surface of the ice sheet. Echo signals are received by two spaced apart in a vertical plane receiving acoustic antennas A ₁ and A ₂ . Echo signals from the closest points on the surface of the ice come first to the antennas, then from increasingly distant points on the irradiated strip of the bottom surface of the ice.

After receiving the echo from the farthest point of the irradiated strip of the lower ice surface, the reception mode ends. To obtain a profile of the ice surface beyond the angle covered by the interferometer’s antenna antennas in the horizontal plane, the underwater object can be moved, after which the interferometer emits another acoustic pulse sounding signal to the side of the water surface. As the interferometer carrier moves along the course line, new adjacent bands of the lower ice surface are irradiated, echo signals from which are received by the interferometer antennas.

Echo signals are received by two spaced apart in a vertical plane receiving acoustic antennas A ₁ and A ₂ . Echo signals from the closest points on the surface of the ice come first to the antennas, then from increasingly distant points on the irradiated strip of the bottom surface of the ice.

If the path difference l, which depends on the base of the interferometer D and θ _i , is equal to an integer number of wavelengths λ _{0 of the} received echo signal, i.e. l = iλ ₀ , where i = 1, 2, 3, ..., then when adding the voltage of the echo signals taken from the outputs of the antennas A ₁ and A ₂ , the total signal will be equal to the sum of the voltages of these signals. If l = (2i-1) λ _0/2, then the sum signal will be equal to their difference. The indicated effect is due to interference of the echo signal from a point on the surface of the ice received by vertically spaced antennas of the interferometer

In the process of receiving and summing the echo signals coming from more and more distant points of the irradiated strip of the ice surface, an interference pattern will be observed at its output of the interferometer, which, being recorded on a brightness recorder (indicator) with a rectangular raster scan in the coordinates “track distance” - “oblique range "Will be an alternating dark and light stripes (interference stripes), as shown in figure 2.

Each interference band in the interference pattern has its own number equal to an integer i of wavelengths λ ₀ characterizing the path difference l = iλ ₀ . In other words, i is the number of the interference band in the interference pattern or the number of the interference lobe in the XN of the antenna of the interferometer, the axis of one of which (i-th) is shown in figa.

The interference fringes are removed from the zero line (the reference point of the slant range) corresponding to the moment the interferometer emits the probe signal, at distances x _i proportional to the corresponding slant ranges r _i to the surface points.

These ranges are measured using a scale ruler. Measurements are taken from the zero line of the interference pattern.

The inclined distance r _i to the point of intersection of the ice surface with the axis of the i-th interference lobe is related to the height z _{i of} this point on the ice surface relative to the horizontal plane passing through the midpoint of the base of the interferometer by the ratio

$$z_i=r_i\sin {\theta }_i.\text{(one)}$$

In turn, from figa that

$$\sin {\theta }_i=\frac{l}{D}=\frac{i{\lambda }_0}{D}.\text{(2)}$$

Combining (1) and (2) we get

$$z_i=r_i\frac{i{\lambda }_0}{D}.\text{(3)}$$

The horizontal distance L _i from the midpoint of the base of the interferometer to a certain point on the ice surface can be determined by the formula

$$L_i=r_i\sqrt{\mathrm{one}-{\left(\frac{i{\lambda }_0}{D}\right)}^2}.\text{(four)}$$

, выполнить расчеты по определению высот z_i и горизонтальных дальностей L_i, используя выражения (3) и (4).Thus, the interference pattern is uniquely associated with the relief of the lower surface of the ice and can be used to determine heights and horizontal ranges in a wide field of view. To do this, it is necessary to determine the numbers of interference fringes i, measure the inclined ranges r _i and, according to the relation known for this interferometer $$\frac{{\lambda }_0}{D}$$

, perform calculations to determine the heights z _i and horizontal ranges L _i using expressions (3) and (4).

Using the values of rainfall ice values z _i d _i calculated heights at the respective points of the bottom surface of the ice and on the corresponding horizontal distances L _i by the formula

$$d_i=h_0-z_i.\text{(5)}$$

where h ₀ is the depth of the middle of the base of the interferometer relative to the surface of the water, calculated by the formula h ₀ = (p-p _atm ) k ₁ k ₂ , where p _atm is the atmospheric pressure above the ice surface at the point of location of the object, k ₁ is the average correction over vertical section, the density of sea water ρ and k ₂ - gravity correction, respectively. The ice thickness H _{i is} calculated from the values of ice precipitation d _i using the linear regression equation of the form

$$H_i\left(\mathrm{from}m\right)=a{d}_i\left(\mathrm{from}m\right)+b\left(\mathrm{from}m\right),\text{(7)}$$

where a and b are empirical regression coefficients that take into account seasonal changes in the density of floating ice and the height of the snow cover on it, for each of the three main seasons of the annual cycle can be defined as - for the summer season (June 16 - September) a = 0.83, b = 39.2, for the fall season (October-November) a = 1.084, b = 0.6 and the winter season (December - June 15) a = 1.070, b = 4.6 [3].

The height of floating ice e, relative to the surface of the water, is calculated as the difference of each pair of values of its thickness and precipitation at points on the surface using the formula

$$e_i=\left(H_i-d_i\right).\text{(8)}$$

As a result, using the method described above, it is possible to determine the morphometric characteristics of the floating ice cover (sediment, thickness, height, profiles of the lower and upper surfaces) not only in a wide field of view above the carrier, characterized by the value of L _i , but also by the ice surface area with high accuracy, due to the exception of errors in estimating the thickness of ice arising as a result of seasonal changes in the density of floating ice and the height of the snow cover on it.

Information sources

1. Borodachev V.E., Gavrilo V.P., Kazan M.M. Glossary of marine ice terms. St. Petersburg: Gidrometeoizdat, 1994 .-- 138 p.

2. Bogorodsky A.V., Ostrovsky D.B. Hydroacoustic navigation and search and research facilities. S-Pb .: Publishing house of St. Petersburg GETU "LETI", 2009.224 p.

3. Mironov E.U., Senko EP On the relationship of thickness and precipitation of ice // Transactions of AANII. - 1995.V.435. - S. 47-54.

4. Baras S.T. Research and development of sonar interferometer for cartographic bottom surveying in a wide field of view. Dis ... cand. tech. sciences / OKB "Reef". G. Beltsy, 1981. - 210 p.

Claims (3)

1. A method for remote determination of precipitation, thickness and height of ice, comprising emitting a sonar emitting antenna from an underwater object in the direction of the surface of the reservoir of sounding signals, receiving acoustic echo signals reflected by the water / ice interface, and simultaneously measuring the absolute hydrostatic pressure p to the sonar using a hydrostat characterized in that an interferometer is used as a sonar, the receiving antennas of which are narrow in the horizontal and wide in the vertical plane x directional characteristics (XI) and spaced vertically by a distance D, which is the base of the interferometer, receive echo signals by both receiving antennas in the range of angles covered by their XN, the distance between the zero line corresponding to the middle of the interferometer base and the middle of the interference band corresponding to the interference pattern is measured points of reflection from the bottom ice surface of the received echo signals, proportional to the distance of these points of reflection from the middle of the base of the interferometer, using rulers, determining the inclined ranges r _i of the reflection points of the echo signal to the middle of the interferometer base, according to the formula $$z_i=r_i\frac{i{\lambda }_0}{D}$$

, where i = 1, 2, 3 ... is the number of the interference band counted from the zero line on the interference pattern corresponding to the moment of radiation of the probing signal, λ ₀ is the wavelength of the received echo signal, the height z _{i of} each ith reflection point from the lower surface is determined ice relative to the horizontal plane passing the middle of the base of the interferometer according to the formula $$L_i=r_i\sqrt{\mathrm{one}-{\left(\frac{i{\lambda }_0}{D}\right)}^2}$$

determine the horizontal distance L _i from the middle of the base of the interferometer to each i-th reflection point, using the values of height z _i calculate ice precipitation d _i at each i-th reflection point from the bottom surface of the ice and at the corresponding horizontal distance L _i using the formula d _i = h ₀ -z _i , where h ₀ is the depth of the middle of the base of the interferometer relative to the surface of the water, calculated by the formula h ₀ = (pp _atm ) k ₁ k ₂ ,
where p _atm - atmospheric pressure above the ice surface at the point of location of the object;
k ₁ - correction for the average vertical density of sea water ρ and k ₂ - gravity correction, respectively, calculate the ice thickness H _i using the linear regression equation of the form H _i (cm) = ad _i (cm) + b (cm),
where a and b are empirical regression coefficients that take into account seasonal changes in the density of floating ice and the height of the snow cover on it, for each of the three main seasons of the annual cycle, at each i-th point, the height of the floating ice e _i relative to the surface of the water is calculated as the difference its thickness and precipitation at surface points using the formula e _i = (H _i -d _i ) and, according to the obtained L _i , d _i and e _i , construct profiles of the lower and upper surfaces of the voiced section of floating ice in the field of view corresponding to the range of angles, covered by directivity characteristics of the interferometer. 2. The method according to claim 1, characterized in that the radiating antenna is located at the midpoint of the base of the interferometer. 3. The method according to claim 1, characterized in that the empirical regression coefficients are determined for the summer season (June 16-September) a = 0.83, b = 39.2, for the autumn season (October-November) a = 1.084, b = 0.6 and the winter season (December - June 15) a = 1.070, b = 4.6.

Images