1. Charles M. Pearcy II, 1Lt, USAF MR3570 17 Sep 04
A Cursory Verification of the Target Acquisition Weapons Software (TAWS) Water Background Algorithms.
Charles M. Pearcy II, 1Lt, USAF
MR3570
17 Sep 04

2. Overview Importance of TAWS Data TAWS Water Algorithms
Density Differences
Water Clarity
Conclusion

3. Importance of TAWS How soon will you see the target?
How soon will the enemy see you?
Change the question
Why did the munition miss? To
Which munition should I use?

4. Data Used UDAS, Rawinsondes, sfc obs for TAWS weather files.
Used the spar pyroheliometer for light attenuation measurements
Used 4 different CTD sites upcast of the top 5m.
For variables in density calculations
For light attenuation measurements

5. TAWS Water Algorithms Three forms of water background.
Soil Moisture (vegetation & bare soil routines)
Swamp/Marsh routines
Water only routines
Water only routines are the focus
Three inputs have an impact
Weather
SST
Water clarity

6. TAWS Water Algorithms Create 15 Layer water column .6m-5m
Layer 15 properties based on residual energy
Mid-layers
based mainly on clarity & layer exchanges
Properties
.6m layer based mainly on weather inputs
Initialize layer density based on average SST
Updated surface temp is background temp
Mixing based on penetrative convection and heat differences

7. TAWS Water Algorithms Solar Forcing .6m 5m Residual energy
Difference in temperature between background
and target determine it’s detection range.
.6m
Turbid
Clear
New Background Temperature Determined
Heat absorption and transmittance in each layer
Convective mixing 5m
Residual energy

8. Initialize layer density based on average SST
Density Differences
Initialize layer density based on average SST
TAWS assumes rv to be constant across all layers (top 5m of water)
2 of 4 cases of CTD data this was exactly true
2 of 4 cases accurate to within .5kg/m^3
TAWS estimates the density of water at all levels based on a 30hr SST average.
rv = 1000 – *(ABS(AveSST-4)^1.68)
Note density is always less than 1000 kg/m^3, this is a fresh water calculation.

9. Density Differences 2.5% error in Density calculations
Site
CTD Density kg/m^3
TAWS Density kg/m^3
Difference
kg/m^3
Percent Error
B037
1024.3
998.6
25.7
2.509
B039
1024.2
25.6
2.4995
B052
1024
998.4
2.500
B054
1023.5
25.1
2.4524
2.5% error in Density calculations
rv is used in 45 calculations and variables affected by it in 433 calculations.

10. based mainly on clarity & layer exchanges
Water Clarity
Mid-layers
based mainly on clarity & layer exchanges
TAWS uses 2 user determined settings for water clarity.
Clear—valued at .05
Turbid—valued at 1.00
TAWS uses clarity exclusively to approximate heat gain due to solar energy exchange processes for the sub layers (.91m-4.69m).

11. Water Clarity Solar Forcing Residual energy Clear Turbid
Heat absorption and transmittance in each layer
Residual energy

12. Water Clarity Clear setting attenuation of .05
Turbid setting has attenuation of 1.00
Took light values (einsteins/sec/m^2) from CTD on upcast and SPAR
CTD/SPAR to get actual light attenuation.

13. Water Clarity
Average light attenuation for all cases and all layers .81
The ocean was more turbid than clear.
Testing TAWS runs for all 4 CTD sites showed almost no difference in detection range due to changing between turbid and clear water.

14. Conclusions Keeping in mind the limited sample size.
Assuming Density is constant for the top 5m of the ocean is a good approximation.
Assuming fresh water in place of sea water may be a problem. Direct manipulation of the code would be necessary.
Turbid vs. clear water only made negligible differences in these cases.

15. Recomendations
Working with TAWS source code is difficult, performance of the overall model on a specific output would be better than nuts and bolts of source code.
For example, determining whether a water background or a swamp/marsh background is more accurate over a kelp forest and/or plankton blooms.

16. References TAWS Source Code, provided by Dr. Andreas Goroch, NRL
SEAWATER: A Library of MATLAB Computational Routines for the Properties of Sea Water. CSIRO Marine Laboratories, provided by Tarry Rago