Environmental Impact on Mine Hunting in the Yellow Sea using ...
Environmental Impact on Mine Hunting in the Yellow Sea using the CASS/GRAB Model Lt Carlos J. Cintron Purpose Purpose of this study is to determine the necessity of a near real time ocean modeling capability such as MODAS for Mine Hunting applications in shallow water regions. AN/SQQ-32 Mine Hunting Sonar System The CASS/GRAB Acoustic model input file used in this study was designed to simulate the Acoustic Performance of the AN/SQQ-32. The AN/SQQ-32 is the key mine hunting component of the U.S. Navys Mine Hunting and Countermeasure ships. Detection Sonar and Classification Sonar Assembly Yellow Sea Bottom Sediment Chart Four Bottom Sediment types were chosen for this Study 1. Mud 2. Sand 3. Gravel 4. Rock Yellow Sea Bottom Topography Water
depth in most of the region is less than 50 m. m Within 50 km of the Korean coastline the average water depth is 20 m. m Seasonal Temperature Profile Structures (a) Winter and Fall Temperature Profile Structure. Isothermal (b) Spring and Summer Temperature Profile Structure. Multi-layer Mixed layer Thermocline Deep Layer Oceanographic Data Sets Master Oceanographic Observational Data Set (MOODS) Generalized Digital Environmental Model (GDEM) Modular Ocean Data Assimilation System (MODAS) Master Oceanographic Observational Data Set (MOODS) Historical world wide observational oceanographic profile data base dating back to 1920. Consist of:
Temperature only profiles Both Temperature and Salinity Profiles Sound Speed profiles Surface Temperatures Biggest limitation is its irregular distribution over time and space. Generalized Digital Environmental Model (GDEM) Gridded Climatological Data derived from MOODS. Global GDEM has a 30 resolution U.S. Navys Operationally important areas contain resolutions of 20 and 10. 10 Contains 3, 6, and 12 month data sets. Modular Ocean Data Assimilation System (MODAS) Climatological MODAS (Static) Gridded Climatological Data derived from MOODS Near
real time Synthetic MODAS (Dynamic) Inputs Satellite SST and SSH into Climatology via model algorithms to produce synthetic Temperature and Salinity fields which are in turn used to produce 3-Dimensional Sound Speed Fields. MIODAS becomes degraded in shallow water regions because SSH is not entered into the model. Altimetry is not entered into the MODAS model in waters less the 150 m due to satellite orbit errors and other model corrections which amplify the error levels near land. Comprehensive Acoustic Simulation System/Guassian Ray Bundle (CASS/GRAB) CASS/GRAB is an active and passive range dependent propagation, reverberation, and signal excess acoustic model that has been accepted as a Navy Standard for the frequency bands of 600 Hz to 100 kHz. kHz CASS/GRAB Model Description The CASS model is the range dependent improvement of the Generic Sonar Model (GSM). CASS performs signal excess calculations. The Grab model is a subset of the CASS model and its main function is to compute eigenrays and propagation loss as inputs in the CASS signal excess calculations. CASS Comprehensive Acoustic
System Simulation Propagation Model 1: FAME Propagation Model 2: GRAB Gaussian Ray Bundle Environmental Interpolations Environmental Model Interpolations Surface and Bottom Forward Loss Volume Attenuation Sound Speed Algorithms Propagation Model 3: COLOSSUS Propagation Model 4: AMOS equations Backscatter Models Reverberation Noise Models Signal to Noise Signal Excess Graphic Displays System Parameters (Beamforming) OAML GRAB v1.0 Call GRAB Comprehensive Acoustic Simulation System/Guassian Ray Bundle (CASS/GRAB) In the GRAB model, the travel time, source angle, target angle, and phase of the ray bundles are equal to those values for the classic ray path. The main difference between the GRAB model and a classic ray path is that the amplitude of the Gaussian ray bundles is global, affecting all depths to some degree whereas classic ray path amplitudes are local. GRAB calculates amplitude globally by distributing the amplitudes according to the Gaussian equation ,0 2 2 pr , r exp 0.5 ( z z ) /
2 Generic Sound Speed Profile Mixed layer Surface duct may be generated with a negative shift in SST Main Thermocline Deep Sound Channel Axis Deep Isothermal Layer Monthly and Annual Mean Sound Speed -40 -20 1485 1490 1495 -40 1470 1475 1480 1485 1490 1495 1470 1475 1480 1485 1490 1495 -20 -20 -20 -40 Jun
Apr/ Depth (m) Sound Speed versus Depth (Sand Bottom) 0 Mar Sound Speed versus Depth (Sand Bottom) 0 Monthly Annual Mean -20 Feb Jan/ Depth (m) comparison for Sand bottom for all 12 months -40 1490 1495 1500 SPEED (m/s) 1500 1510 1520 -40 1488 1490 1492 1494 1496 1498 SPEED (m/s) Speed profiles transition from Isotherm in the winter to Multi-layer in the Summer AN/SQQ-32 Concept Variable depth high frequency sonar system Sonar can be place at various positions in the water column to optimize
the detection of either a moored or bottom mines. In complimenting the AN/SQQ-32 mine hunting sonar system concept in this Study Two source depths were chosen. 25 ft (Above the Mixed Layer if present) 125 ft (Within or below the Mixed Layer if present) GDEM Seasonal Variability for Signal Excess GDEM /January/ Sand/ SD = 25 ft GDEM /June/ Sand/ SD = 25 ft GDEM Seasonal Variability for Signal Excess GDEM /January/ Sand/ SD = 125 ft GDEM /June/ Sand/ SD = 125 ft Acoustic Transmission Under Severe Weather Events Track of Tropical Depression Kai-Tak over the Yellow Sea for 10-11 July 2000 Satellite Images of Tropical Depression Kai-Tak July 8, 2000 Tropical Cyclone over the East China Sea July 10, 2000 Tropical Depression
over the Yellow Sea July 9, 2000 Tropical Cyclone over the Northern East China Sea July 11, 2000 Tropical Depression over the Northern Yellow Sea Sound Speed and Maximum Detection Range Differences for a Mud Bottom region and a Source Depth of 25 ft Sound Speed and Maximum Detection Range Differences for a Mud Bottom region and a Source Depth of 125 ft Sound Speed and Maximum Detection Range Differences for a Sand Bottom region and a Source Depth of 25 ft Sound Speed and Maximum Detection Range Differences for a Sand Bottom region and a Source Depth of 125 ft Significant Acoustic Differences in detection ranges as Defined by the Mine Warfare Community A Significant Difference in detection range ranges as Defined SignificantAcoustic Acoustic Differences in detection as by the Mine :
Defined by Warfare the MineCommunity Warfare Community: Position of Detection ranges of Mine relative to Source If Both Detection Ranges are less than 600 yards If either of The THEDetection DETECTION Ranges Ranges are greater are than greater or than equalor toequal 600 to 600 yards yards A significant Acoustic Difference exists if: Detection Ranges > 100 Yards Detection Ranges > 100 Yds Detection Ranges > 200> Yards Detection Ranges 200 Yds Maximum Significant Acoustic Difference in detection ranges for MODAS before and after the Tropical Depression (SD =25ft) Source Depth = 25 ft Source
Depth = 25 ft Target Depth Mud Mud Target Depth July 10 July 7 July 10 July 7 26 ft 26 ft Bottom Bottom Sand Sand July 15 July 10 July 10 July 7 July 15 July 10 July 15 July 10 July 10 July 7 July 15 July 10 Lat Lon 124.0E Lat36.5N 36.5N Lon 124.0E 490 yds Figure 62 and 63 None None None None
None None None None None None None None Lat 36.5N Lon Lon 124.0E Lat 36.5N 124.0E 490 yds Figure 62 and 63 490 yds 490 yds Maximum Significant Acoustic Difference in detection ranges for MODAS before and after the Tropical Depression (SD=125ft) Source Depth = 125 ft Source Depth = 125 ft Target Depth Target Mud Mud Depth 26 26ftft Bottom
Bottom Sand Sand July10 10 July July July7 7 July15 15 July July July1010 July 10 10 July July July7 7 July 10 10 July1515 July July None None None None None None None None Lat LonLon 124.0E Lat36.5N 36.5N 124.0E 810 yds Figure 66 and 67
None None Lat Lon 124.0E Lat36.5N 36.5N Lon 124.0E 790 yds Figure 64 and 65 790 yds 810 yds None None Temperature versus Depth (Lat 36.5 N 124.0 E/ Mud Bottom) Temperature and Sound 0 Speed Comparisons -50 Slight Decrease in SST of 0.4 o C was observed between July 7 and 10 Depth (ft) -100 -200 -Possibly due to no SST input into the MODAS model from MCSSTS due to heavy cloud cover during the Tropical Depression. The absence of SSH from Satellite Altimeters may have not allowed MODAS to capture the storms effect to
the mixed layer July 10, 2000 July 7, 2000 July 15, 2000 -250 -300 10 A decrease in SST of 1.9 o C was observed between July 10 and 15. 12 14 16 18 20 Temperature (Degrees C) 22 24 Sound Speed versus Depth (Lat 36.5 N 124.0 E/ Mud Bottom) 0 -50 -100 Depth (ft) -SST from MCSSTS may have been available for input for July 15, but effects of the Tropical depression on SST may have weaken by then. -150 -150 -200 July 10, 2000 July 7, 2000 July 15, 2000
-250 -300 1490 1495 1500 1505 1510 1515 Sound Speed (m/s) 1520 1525 1530 Ray Traces of Profiles with Significant Acoustic Differences Moored Mine July 7, 2000/ Mud / DR = 490yds Source Depth = 25 ft July 10, 2000/ Mud/ DR = 770 yds July 15, 2000/ Mud /DR =490yds Signal Excess Contours of Profiles with Significant Acoustic Differences Moored Mine July 7, 2000/ Mud /DR = 490yds Source Depth = 25 ft July 10, 2000/ Mud/ DR = 770 yds July 15, 2000/Mud/DR = 490yds Ray Traces of Profiles with Significant Acoustic Differences July 7, 2000/Mud/DR = -775 yds Bottom Mine Source Depth = 125 ft July 10, 2000/ Mud/ DR = 0 yds
July 15, 2000/Mud/DR = -810 yds Signal Excess Contours of Profiles with Significant Acoustic Differences Bottom Mine July 7, 2000/Mud/DR = -775 yds Source Depth = 125 ft July 10, 2000/ Mud/ DR = 0 yds July 15, 2000/Mud/DR = -810 yds Maximum Significant Acoustic Differences in detection ranges for MODAS versus MOODS Source Depth = 25 ft Source Depth = 25 ft Target Target Depth Depth= 26 ft 26 ft Month Month Mud Mud Sand Sand 1999 1999 February February Lt 35.0N 123.5E Lt 35.0NLnLn 123.5E 760 yds 760 yds
May May Lt 35.0N 123.0E Lt 35.0NLnLn 123.0E 795 yds 795 yds August August Lt 35.9N 124.4E Lt 35.9NLnLn 124.4E 545 yds 545 yds November November Lt 36.5N 123.0E Lt 36.5NLnLn 123.0E 840 yds 840 yds 2000 2000 Lt 35.0N 123.5E Lt 35.0NLnLn 123.5E 760 yds 760 yds Lt 35.0N 123.0E Lt 35.0NLnLn 123.0E
None None Lt 35.9N Ln 125.8E 765 yds Maximum Significant Acoustic Differences in detection ranges for MODAS versus MOODS Target Depth = 26 ft 26 ft Source Depth = 25 ft Source Depth = 50/ 75/ 125 ft Month Month Mud Mud 1999 1999 February February May May August August November November Sand Sand 2000 2000 1999 1999 20002000 LtLt35.0N 35.0NLnLn123.5E
765 yds May May LtLt 35.0N LnLn 123.5E 36.4N 124.4E 760 yds Sand Sand 1000 yds 225 yds 1000 yds 315 yds 265 yds 205 yds Oceanographic Difference between MODAS and MOODS Targ et Dept h= 26 ft Source Depth = 25 ft MODAS versus MOODS Month Mud Sand February for Mud Bottom Type 1999 2000 1. Oceanographic Difference between MODAS February
and MOODSLt 35.0N Ln 123.5E 760 yds 1999 2000 Differences are due to a deficiency in the MODAS which the MODAS Lt 35.0N Lnclimatology, Lt 35.9N Lngives Lt 35.9N Ln profiles a near bottom positive gradient. 123.5E 125.8E 125.8E (See Text) 760 yds 840 yds 840 yds May 35.0N Ln Lnbottom Lt positive 35.9N gradient Ln Lt 35.9NupLn This near produced 2. How did this affect Lt the Acoustic ModelLt 35.0N 123.0E 795 yds August
Lt 35.9N 124.4E 545 yds Ln 3. Prevalence Novembe of Problems Lt if 36.5N any inLn the r or North East 123.0E Yellow Sea China Sea 840 yds 123.0E 126.0E bending near the bottom. When the126.0E Source was 780 yds 795 yds 810 yds at hull depth both moored and bottom mines detection ranges were over predicted. When the Source was at 125 ft moored mines detection Lt 35.9N Ln over Lt predicted 35.9N and Ln bottom Lt 35.9N ranges were mines Ln 124.4E 124.8E 124.8E detection ranges were under predicted. 535 yds 820 yds 815 yds This problem
was approximately 15 Ln % Lt 36.5N Ln Lt present 35.9N inLn Lt 35.9N of the MODAS profiles in the Yellow Sea. 123.0E 125.8E 125.8E 840 yds 765 yds 765 yds Near Bottom Positive Gradient Error Mud bottom/ February/ 35.0 N 123.5 E/ Source Depth = 125 ft MODAS MOODS Near Bottom Positive Gradient Error Mud bottom/ February/ 35.0 N 123.5 E/ Source Depth = 125 ft MODAS MOODS Oceanographic Difference between MODAS and MOODS SourceMOODS Depth = 25 ft MODAS versus Target Depth = 26 ft November/ Mud Bottom Mud
Month 1. Oceanographic Difference between MODAS and MOODS 1999 February Lt 35.0N Ln 123.5E 760 yds 2. How did this affect the Acoustic Model May Lt 35.0N Ln 123.0E 795 yds August Lt 35.9N Ln 124.4E 545 yds Sand Differences were due to the presence of a surface duct when the source in both 2000 depth was at 25 ft. When 1999 there was a surface duct 2000 profiles, it was much stronger in the MOODS profile for most cases. In most cases, MODAS produced surface ducts that were weaker than would be expected. MODAS weakens the gradients Lt 35.0N Lt 35.9N Ln inLn the123.5E thermocline. Lt 35.9N Ln 125.8E 760 yds 840 yds 125.8E 840 yds The surface ducts produce greater detection ranges for a moored mine. The weaker surface ducts produced by MODAS sometimes under predicted the detection range of a moored mine. No Lt 35.0N Ln 123.0E
Lt 35.9N Ln 126.0E Lt 35.9N Ln significant acoustic differences were observed for a bottom mine 780 yds 795 yds 126.0E due to the presence or absence of a surface duct. When the source 810 yds depth was within the thermocline the weaker thermocline gradients produced by MODAS caused less down bending of sound propagation. This produced weaker caustics due to less Lt 35.9N Ln 124.4E Lt 35.9N Ln 124.8E Lt 35.9N Ln focusing of sound propagation, which in turn caused an under 535 yds 820 yds 124.8E prediction of moored mines. (See Text) 815 yds The weaker surface ducts found in the MODAS profiles cannot be 3. Prevalence of Problems if any in the Yellow Sea or November Lt 36.5N Ln 123.0E Lt 36.5N Ln 123.0Eto be a problem Lt 35.9Nwithout Ln 125.8E 35.9N determined performingLta study of the Ln North East China Sea 840 yds 840 ydsMODAS climatology. 765Weaker yds MODAS thermocline 125.8E gradients 765MODAS
yds were observed in approximately over 75 % of the profiles used in this study. Weakening of Surface Duct Mud bottom/ November/ 36.5 N 123.0 E/ Source Depth = 25 ft MODAS MOODS Weakening of Thermocline Mud bottom/ November/ 35.0 N 123.0 E/ Source Depth = 125 ft MODAS MOODS Maximum Acoustic Difference in detection ranges for MODAS Versus MODAS plus Gaussian error in Sound speed February Target Target Depth = Depth 26 ft Source Depth = 25 ft Source Depth = 25 ft Month Mud Mud 1999 February May 26 ft Bottom Target Target Depth = Depth 26 ft 1 Lt35.4N Ln 124.4E
440 Lt 35.9N Lnyds 124.8E 820 Ltyds 36.4N Ln 124.6E 375 yds 2000 Lt 35.9N Ln 125.8E 840 yds 10 Lt 35.9N Ln 126.0E Lt 36.4N Ln 124.4E 810 yds yds Lt380 35.9N Ln 124.8E 815 yds Lt 36.4N Ln 124.6E 755 yds Histograms of the Acoustic Difference Distribution throughout the Water Column for Source Depth = 125 ft, Mud bottom February 15, 2000 August 15, 2000 Effect of Sound Speed Error at Source Depth No Error +1 m/s Error -1 m/s Error Conclusion Capability of CASS/GRAB model Strong seasonal variability in acoustic transmission (detection range, signal excess) . Effect of the tropical cyclone on acoustic transmission Error propagation from sound speed profile to signal excess Capability of MODAS
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