Noise and reverberation sonar range computer
United States Patent 3924104
This disclosure is directed to a slide rule type device for determining the noise and reverberation which limits sonar performance. The device includes a base and cursor upon which related information has been placed. The cursor is operatively related with the data on the base such that associated information may be used for determining noise and reverberation for sonar equipment.
US Patent References:
Slide rule
Cole - October 1951 - 2569454
Submarine depth computer
Bauer - June 1961 - 2967662
Sonar slide rule
Barron - August 1966 - 3266721
Slide rule
Cole - October 1951 - 2569454
Submarine depth computer
Bauer - June 1961 - 2967662
Sonar slide rule
Barron - August 1966 - 3266721
Application Number:
05/154616
Publication Date:
12/02/1975
Filing Date:
06/18/1971
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
235/89R
International Classes:
G06C3/00; G06C3/00
Field of Search:
235/61R,61.5R,61.5DF,61.5T,61.5B,69,70,61B,89R
Primary Examiner:
Feinberg, Samuel
Attorney, Agent or Firm:
Sciascia, Branning Arthur Crane Melvin R. S. L. L.
Claims:
What is claimed and desired to be secured by Letters Patent of the United States is
1. A device for determining noise and reverberation that limits sonar performance, which includes,
2. A device as claimed in claim 1; wherein,
3. A device as claimed in claim 2; which includes,
4. A device as claimed in claim 3; which includes,
1. A device for determining noise and reverberation that limits sonar performance, which includes,
2. A device as claimed in claim 1; wherein,
3. A device as claimed in claim 2; which includes,
4. A device as claimed in claim 3; which includes,
Description:
BACKGROUND OF THE INVENTION
This invention relates to a hand operated computation device and more particularly to a computation device for determining and correcting for noise and reverberation which limits sonar operation.
SUMMARY OF THE INVENTION
This invention is directed to a hand operated computer device having a base upon which noise and reverberation data has been placed in combination with range in Kiloyards, thermal depth in feet, and frequency data have been placed. The cursor includes thereon noise and reverberation curves in combination with spaced parallel lines which are asymtotes to the curves. The cursor also includes spaced lines from which ranges may be obtained for desired probabilities of detection.
STATEMENT OF THE OBJECTS
It is therefore an object of the present invention to provide a hand operated computation device for computing ambient noise and reverberation which limits sonar performance.
Another object is to provide a simple efficient, inexpensive computation device for computing noise and reverberation which limits sonar performance.
Still another object is to provide a noise and reverberation computation device which may be used by unskilled as well as skilled personnel.
Other objects and advantages of the invention will become obvious to others upon reading the following description of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a top view of the device;
FIG. 2 illustrates the base with data thereon; and
FIG. 3 illustrates a separate view of the cursor.
DESCRIPTION OF THE DRAWINGS
Now referring to the drawings there is shown by illustration a computation device for correcting the performance of a sonar in determining range. As shown, the device includes a base 10, upon which data has been placed. Above the base there is located a slidable cursor 11 which includes reference lines as well as frequency correction information.
The base may be formed of a solid material such as plastic, metal, wood or any other desired material and of rectangular shape. Across the length of the bottom, there are placed four linear scales 13-16 of numerical information graduated in accordance with data obtained by well known equations for well known sonar equipment. Two of the linear scales 13 and 15 are for noise and scales 14 and 16 are for reverberation. The letters of R1, N1, R2, and N2 refer to noise and reverberation, as limiting factors, and the numbers by the letters refer to a two-dimensional or a one-dimensional transducer. The figures on the scales are formed by the following equations:
R1 - reverberation for a one-dimensional transducer ##EQU1## N1 - Noise for one-dimensional transducer ##EQU2## R2 - Reverberation for two-dimensional transducer ##EQU3## N2 - Noise for two-dimensional transducer ##EQU4## where P = Acoustic power
A = transducer Area (cm) 2
t = pulse length (milliseconds)
n = sea state, characterizing ambient noise
l = transducer length (cm)
θ = aspect angle from 0° to 90°
Cos θ = Cos θ from 0° to 80°
= 0.173 from 80° to 90°
f = frequency
fn 1, fn 2 = Optimum frequency for noise limited range
V = target speed (Knots)
V = speed of carrier (knots for airborne equipment)
If the directivity is D at a frequency f, then the area A may be taken from 10 log A = 32.7 + D -20 log f.
If the directivity is D at a frequency f, then the length may be from 10 log l = 18.8 + D -10 logf.
Immediately above the scales on the base, there is a logarithmic coordinate system tilted at a 45° angle with respect to the linear scales on the bottom portion of the base. The lines 17 of the logarithmic scale that extend upwardly and to the right indicate the thermal depth, d, values in feet (20-400) which are shown along the bottom near the edge of the scales. The lines 18 extending upwardly to the left indicate range in Kiloyards, the values are shown along the upper left and right edges of the coordinate system.
Further, there is shown a plurality of parallel lines 21 extending from the thermal depth scale upwardly to a curved line 22. The curved line is used to determine the range of a target below the thermocline. The curve is such that the parallel lines extend from the edge of the curved line ends at the corresponding range. The curved line is determined by well known sonar formula which relates depth to range.
The two straight lines Fn1 and Fn2 serve to determine the optimum frequency for a noise limited range. The lines are determined for specific equipment and the lines relate depth to frequency.
The noise and reverberation scalar information is related to the thermal depth in feet and range in Kiloyards by use of a cursor which is moveable along the base. The cursor contains thereon three curves 26, 27, and 28 which extend from the upper left corner toward the bottom and right side. The curves are formed from data relating the noise and reverberation to the thermal depth in feet and the range in Kiloyards. The cursor includes a vertical line 31 that extends across all of the scalar lines. This line is used in determining the nominal range, that is, the range obtained with a 50% probability of detection. The short vertical lines 32-35 (10, 30, 70 and 90) on each side of the long line for each of the scalar lines serve to find the ranges obtained with the respective probabilities. The slope of the lines on the cursor are such that when the probability line selected is placed over the corresponding noise or reverberation scale, the point of interception of the thermal depth line with the corresponding curve will give the range. The range of operation will be with the smaller range, as determined for the noise and reverberation, corresponding to the conditions. The noise and reverberation may be determined by the above formulas depending on the equipment and the different parameters that affect the sonar signal.
Operation of the computation device for determining sonar range with equipment operating with the following parameters;
P = 32W ; t = 120 milisec f = 20Kc ; N = 4 A = 420cm 2 ; Thermal depth - 150 feet
target speed = 3 Knots; θ = 60° (target above the thermocline) is as follows:
Step 1:
Calculate characteristic figures N2 and R2 from the formulas previously given above for the above given conditions:
N2 = 73.4db
R2 = 29.2db
These values may also be obtained by use of a chart which shows a direct relationship between ships speed, target speed and the Figure of merit.
Step 2:
Slide the cursor 1 until the long probability mark "50" (line 31) is set directly over 73.4 on scale 13 (N2).
Step 3:
Follow line d = 150 up to its intersection with curve 26 (N2). Read the value of Range r of this point which is found to be 4.2 Ky. This is the noise limited range r.
Step 4:
Move the cursor so that the "50" line is over 29.2 of the R2 scale, follow line d = 150 to its intersection with curve 28 R1R2). Read the Range value r of this point which is 3.9 kyd. This is the reverberation limited range, r R at optimum frequency.
Step 5:
Estimate the correction to r N corresponding to the operational frequency. No such correction is required for reverberation limited range found by the computer.
Step 6:
Find the optimum frequency f o by following the line r = r n (4.2 ky) to its intersection with the line fn2 going right and up from this point, read fo on the upper edge at 17 Khertz.
Step 7:
The range corresponding to an operating frequency fl, r f is smaller than the range at optimum frequency, r n by a fraction b which is for a rough estimate;
b + 0.05 (k 2 - 1) when K = f/fo for f<fo and fo/f for f>fo.
If f deviates from o by less than 20% the range correction is smaller than 2%.
For more precise information, form the ratio f/fo and read with this value as abscissa, the ordinate from curve R2(db) subtract this from N2 and read r for the reduced characteristic figure. This is the noise limited range rf for a frequency f. In the example fo=20, f=17 for this abscissa C2 has the f/fo = 1.18 value of 0.6 db. The reduced characteristic figures is 73.4 - 0.6 = 72.8; the noise limited range is 4.15 ky instead of 4.2 kyd.
EXAMPLE 2
With data as in example 1, but target below the thermocline, proceed as follows:
Step 1:
Set cursor at N2 = 73.4.
Step 2:
From the point 150 on d scale, follow a line to the left and up to its intersection with the curve 22 marked "target below thermocline". From this point follow the line d = constant (62 in the example) up to the intersection with curve N2 giving r N =3.3 Kyds.
Step 3:
apply the correction for non-optimum frequency to r N . Similarly, with the cursor set at R2 = 29.2 follow the line d = 62 to intersection with curve R1R2 giving r R =2.4 Kyd.
EXAMPLE 3:
Data as in Example 1, ranges to be determined for a probability other than 50%. To find the noise limited range for a probability of say 10% slide cursor to a position where the index line "10" belonging to scale N2 is set at 73.4 on scale N2 proceeding as before, one finds r N = 5.0 ky for d = 150 ft. To find the reverberation limited range for a probability of 10%, slide cursor to a position where the indices "10" belonging to scale R2 is set at 29.2 on scale R2 proceeding as in paragraph 5 above, one finds r R = 6.4 Kyd for d = 150 ft. The probability at other % values may be obtained by moving the cursor such that the desired value is over the determined value on the noise and reverberation scales as set forth above.
The curve 30 on the left of the device may be used for determining a correction factor which may be used to find the final operable range as set forth above.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
This invention relates to a hand operated computation device and more particularly to a computation device for determining and correcting for noise and reverberation which limits sonar operation.
SUMMARY OF THE INVENTION
This invention is directed to a hand operated computer device having a base upon which noise and reverberation data has been placed in combination with range in Kiloyards, thermal depth in feet, and frequency data have been placed. The cursor includes thereon noise and reverberation curves in combination with spaced parallel lines which are asymtotes to the curves. The cursor also includes spaced lines from which ranges may be obtained for desired probabilities of detection.
STATEMENT OF THE OBJECTS
It is therefore an object of the present invention to provide a hand operated computation device for computing ambient noise and reverberation which limits sonar performance.
Another object is to provide a simple efficient, inexpensive computation device for computing noise and reverberation which limits sonar performance.
Still another object is to provide a noise and reverberation computation device which may be used by unskilled as well as skilled personnel.
Other objects and advantages of the invention will become obvious to others upon reading the following description of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a top view of the device;
FIG. 2 illustrates the base with data thereon; and
FIG. 3 illustrates a separate view of the cursor.
DESCRIPTION OF THE DRAWINGS
Now referring to the drawings there is shown by illustration a computation device for correcting the performance of a sonar in determining range. As shown, the device includes a base 10, upon which data has been placed. Above the base there is located a slidable cursor 11 which includes reference lines as well as frequency correction information.
The base may be formed of a solid material such as plastic, metal, wood or any other desired material and of rectangular shape. Across the length of the bottom, there are placed four linear scales 13-16 of numerical information graduated in accordance with data obtained by well known equations for well known sonar equipment. Two of the linear scales 13 and 15 are for noise and scales 14 and 16 are for reverberation. The letters of R1, N1, R2, and N2 refer to noise and reverberation, as limiting factors, and the numbers by the letters refer to a two-dimensional or a one-dimensional transducer. The figures on the scales are formed by the following equations:
R1 - reverberation for a one-dimensional transducer ##EQU1## N1 - Noise for one-dimensional transducer ##EQU2## R2 - Reverberation for two-dimensional transducer ##EQU3## N2 - Noise for two-dimensional transducer ##EQU4## where P = Acoustic power
A = transducer Area (cm) 2
t = pulse length (milliseconds)
n = sea state, characterizing ambient noise
l = transducer length (cm)
θ = aspect angle from 0° to 90°
Cos θ = Cos θ from 0° to 80°
= 0.173 from 80° to 90°
f = frequency
fn 1, fn 2 = Optimum frequency for noise limited range
V = target speed (Knots)
V = speed of carrier (knots for airborne equipment)
If the directivity is D at a frequency f, then the area A may be taken from 10 log A = 32.7 + D -20 log f.
If the directivity is D at a frequency f, then the length may be from 10 log l = 18.8 + D -10 logf.
Immediately above the scales on the base, there is a logarithmic coordinate system tilted at a 45° angle with respect to the linear scales on the bottom portion of the base. The lines 17 of the logarithmic scale that extend upwardly and to the right indicate the thermal depth, d, values in feet (20-400) which are shown along the bottom near the edge of the scales. The lines 18 extending upwardly to the left indicate range in Kiloyards, the values are shown along the upper left and right edges of the coordinate system.
Further, there is shown a plurality of parallel lines 21 extending from the thermal depth scale upwardly to a curved line 22. The curved line is used to determine the range of a target below the thermocline. The curve is such that the parallel lines extend from the edge of the curved line ends at the corresponding range. The curved line is determined by well known sonar formula which relates depth to range.
The two straight lines Fn1 and Fn2 serve to determine the optimum frequency for a noise limited range. The lines are determined for specific equipment and the lines relate depth to frequency.
The noise and reverberation scalar information is related to the thermal depth in feet and range in Kiloyards by use of a cursor which is moveable along the base. The cursor contains thereon three curves 26, 27, and 28 which extend from the upper left corner toward the bottom and right side. The curves are formed from data relating the noise and reverberation to the thermal depth in feet and the range in Kiloyards. The cursor includes a vertical line 31 that extends across all of the scalar lines. This line is used in determining the nominal range, that is, the range obtained with a 50% probability of detection. The short vertical lines 32-35 (10, 30, 70 and 90) on each side of the long line for each of the scalar lines serve to find the ranges obtained with the respective probabilities. The slope of the lines on the cursor are such that when the probability line selected is placed over the corresponding noise or reverberation scale, the point of interception of the thermal depth line with the corresponding curve will give the range. The range of operation will be with the smaller range, as determined for the noise and reverberation, corresponding to the conditions. The noise and reverberation may be determined by the above formulas depending on the equipment and the different parameters that affect the sonar signal.
Operation of the computation device for determining sonar range with equipment operating with the following parameters;
P = 32W ; t = 120 milisec f = 20Kc ; N = 4 A = 420cm 2 ; Thermal depth - 150 feet
target speed = 3 Knots; θ = 60° (target above the thermocline) is as follows:
Step 1:
Calculate characteristic figures N2 and R2 from the formulas previously given above for the above given conditions:
N2 = 73.4db
R2 = 29.2db
These values may also be obtained by use of a chart which shows a direct relationship between ships speed, target speed and the Figure of merit.
Step 2:
Slide the cursor 1 until the long probability mark "50" (line 31) is set directly over 73.4 on scale 13 (N2).
Step 3:
Follow line d = 150 up to its intersection with curve 26 (N2). Read the value of Range r of this point which is found to be 4.2 Ky. This is the noise limited range r.
Step 4:
Move the cursor so that the "50" line is over 29.2 of the R2 scale, follow line d = 150 to its intersection with curve 28 R1R2). Read the Range value r of this point which is 3.9 kyd. This is the reverberation limited range, r R at optimum frequency.
Step 5:
Estimate the correction to r N corresponding to the operational frequency. No such correction is required for reverberation limited range found by the computer.
Step 6:
Find the optimum frequency f o by following the line r = r n (4.2 ky) to its intersection with the line fn2 going right and up from this point, read fo on the upper edge at 17 Khertz.
Step 7:
The range corresponding to an operating frequency fl, r f is smaller than the range at optimum frequency, r n by a fraction b which is for a rough estimate;
b + 0.05 (k 2 - 1) when K = f/fo for f<fo and fo/f for f>fo.
If f deviates from o by less than 20% the range correction is smaller than 2%.
For more precise information, form the ratio f/fo and read with this value as abscissa, the ordinate from curve R2(db) subtract this from N2 and read r for the reduced characteristic figure. This is the noise limited range rf for a frequency f. In the example fo=20, f=17 for this abscissa C2 has the f/fo = 1.18 value of 0.6 db. The reduced characteristic figures is 73.4 - 0.6 = 72.8; the noise limited range is 4.15 ky instead of 4.2 kyd.
EXAMPLE 2
With data as in example 1, but target below the thermocline, proceed as follows:
Step 1:
Set cursor at N2 = 73.4.
Step 2:
From the point 150 on d scale, follow a line to the left and up to its intersection with the curve 22 marked "target below thermocline". From this point follow the line d = constant (62 in the example) up to the intersection with curve N2 giving r N =3.3 Kyds.
Step 3:
apply the correction for non-optimum frequency to r N . Similarly, with the cursor set at R2 = 29.2 follow the line d = 62 to intersection with curve R1R2 giving r R =2.4 Kyd.
EXAMPLE 3:
Data as in Example 1, ranges to be determined for a probability other than 50%. To find the noise limited range for a probability of say 10% slide cursor to a position where the index line "10" belonging to scale N2 is set at 73.4 on scale N2 proceeding as before, one finds r N = 5.0 ky for d = 150 ft. To find the reverberation limited range for a probability of 10%, slide cursor to a position where the indices "10" belonging to scale R2 is set at 29.2 on scale R2 proceeding as in paragraph 5 above, one finds r R = 6.4 Kyd for d = 150 ft. The probability at other % values may be obtained by moving the cursor such that the desired value is over the determined value on the noise and reverberation scales as set forth above.
The curve 30 on the left of the device may be used for determining a correction factor which may be used to find the final operable range as set forth above.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.