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Produced by the NASA Center for Aerospace Information (CASI)
NASA Contractor Report CR-2006-2 14205 

C 

RSA/Legacy Wind Sensor Comparison. 

Part II: Eastern Range 

David A. Short 

Applied Meteorology Unit 

Kennedy Space Center, Florida 

Mark M. Wheeler 

Applied Meteorology Unit 

Kennedy Space Center, Florida 

May 2006
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NASA Contractor Report CR-2006-2 14205 

RSA/Legacy Wind Sensor Comparison. 

Part II: Eastern Range 

David A. Short 

Applied Meteorology Unit 

Kennedy Space Center, Florida 

Mark M. Wheeler 

Applied Meteorology Unit 

Kennedy Space Center, Florida 

National Aeronautics and 

Space Administration 

Kennedy Space Center 

Kennedy Space Center, FL 332899-000] 

May 2006
Acknowledgements 

The authors thank Dr. Francis J. Merceret of the Kennedy Space Center Weather Office for his guidance. 

Available from: 

NASA Center for AeroSpace Information

7121 Standard Drive

Hanover, MD 21076-1320

(301) 621-0390 

This report is also available in electronic form at

http://science.ksc.nasa.gov/amu/
Executive Summary 

The goal of this study was to evaluate the performance of ultrasonic wind sensors being used to replace 

mechanical wind sensors at the Eastern Range (ER). Launch Weather Officers, forecasters, and Range Safety analysts 

need to understand the performance of wind sensors at the ER and Western Range (WR) for weather warnings, 

watches, advisories, special ground processing operations, launch pad exposure forecasts, user Launch Commit 

Criteria (LCC) forecasts and evaluations, and toxic dispersion support. The current ER weather tower wind 

instruments are being changed from Legacy propeller-and-vane sensors to ultrasonic sensors through the Range 

Standardization and Automation (RSA) program. The Legacy sensors measure wind speed and direction 

mechanically. The ultrasonic RSA sensors have no moving parts. These differences in wind measuring techniques 

have been found to cause differences in the statistics of peak wind speed in previous studies. The 45th Weather 

Squadron (45 WS) and the 30th Weather Squadron (30 WS) requested the Applied Meteorology Unit (AMU) to 

compare data between RSA and Legacy sensors to determine if there are significant differences. This report addresses 

the comparison of Legacy and RSA wind speed and direction sensors on the ER. 

An 18-day archive of 1-minute ER Legacy and RSA wind data was used by the AMU in this study. The periodof-record (POR) was 13 - 30 May 2005 from 5 towers: 0002, 0006, 0108, 0313 and 0403. The 5 towers were 

instrumented at numerous levels, ranging from 12 ft to 492 ft. The ER Legacy and RSA data archive covered 24 

hours each day and included 1-minute average wind speed and direction and the peak wind speedldirection used to 

evaluate LCC during operations. 

The Legacy data was provided by a propeller-and-vane system with the vane (direction) and propeller (speed) 

molded into one unit. The RSA wind data was obtained from an ultrasonic-type sensor that derives wind speed and 

direction information from the effect of wind on the transit time of ultrasonic pulses between three electro-acoustic 

transducer pairs, mounted in an equilateral triangle. The data archive for this study included one or two Legacy 

systems, depending on the tower, and one RSA sensor at each level. The Legacy and RSA systems were mounted at 

the same level. Data from a total of 19 RSA sensors, collocated with Legacy speed/direction systems were used. 

The AMU created time series of wind speed and direction for each Legacy and RSA system on each tower at 

each level. The Legacy and RSA time series were then aligned, minute-by-minute. The AMU then used the Legacy 

wind direction information to obtain samples with the Legacy sensors on the upwind side of the tower. This 

procedure was followed to minimize effects of tower obstruction on the sensor inter-comparisons. A total of 357,626 

1-minute comparisons of Legacy versus RSA wind information were obtained after the initial screening process. A 

secondary screening identified anomalous RSA peak wind speed readings on Tower 0108 and data from that tower 

were handled separately. 

The overall comparison of 329,018 minutes of secondary screened data resulted in the following: 

. Overall Average Wind Speed: Legacy 7.72 kts, RSA 8.27 kts, RSA - Legacy = + 0.55 kts 

. Overall Peak Wind Speed: Legacy 9.51 kts, RSA 10.72 kts, RSA - Legacy= + 1.21 kts 

The AMU also examined each Legacy/RSA pairing for consistency in wind speed and wind direction. Four of 

the 19 RSA sensors showed patterns of variability in differences from the Legacy sensors that were outside the norm 

of the other 15 RSA sensors. These 15 RSA sensors were used to define a composite average-Legacy/RSA 

comparison and the peak wind speed data from the same 15 RSA sensors were used to define a composite peakLegacyfRSA wind speed comparison. 

Comparisons of the 15 sensor composite were slightly different than the overall comparison cited above. 

• Composite Average Speed: Legacy 8.09 kts, RSA 8.47 kts, RSA - Legacy = + 0.38 kts 

• Composite Peak Speed: Legacy 9.79 kts, RSA 10.73 kts, RSA - Legacy = + 0.94 kts 

From a technical point of view the small differences in average wind speeds reported by the Legacy and RSA 

sensors are statistically significant, due to the large sample size and small standard deviation of differences in 1-

minute wind speed between the sensors, +1- 0.90 kts. From a practical point of view the differences in peak wind 

speeds are more important, indicating that the change to ultrasonic sensors can be expected to result in an increase in 

reported peak wind speeds. An increase in peak wind speeds would result in a decrease of launch availability, 

depending on the LCC threshold wind speed. For example, the probability of peak wind speeds at 20 kts or less 

using the Legacy data was 95.2%. For the same 20 kt threshold the RSA data showed a probability of 92.3%.
Table of Contents 

Listof Figures....................................................................................................................................................... 5

Listof Tables ........................................................................................................................................................ 6

1. Introduction ..............................................................................................................................................7 

2. Data and Sensor Description...................................................................................................................7 

2.1. Legacy Wind Sensor................................................................................................................................8 

2.2. RSA Wind Sensor....................................................................................................................................8 

3. Analysis Procedure ................................................................................................................................... 9

3.1. Extract Minute-by-Minute.......................................................................................................................9 

3.2. Wind Sector Filter ...................................................................................................................................9 

4. Results ..................................................................................................................................................... 12

4.1. Overall Composite Results: Average and Peak Wind Speeds...............................................................12 

4.2. Sensor-by-Sensor Comparisons.............................................................................................................13 

4.2.1. Conditional Averages...................................................................................................................13 

4.2.2. Difference of Average Wind Speeds............................................................................................14 

4.2.3. Difference of Average Wind Direction........................................................................................15 

4.2.4. Anomalous Peak Wind Speeds from RSA Sensors on Tower 0108 ............................................16 

4.3. Best Composite Results: Average and Peak Wind Speeds....................................................................19 

5. Conclusions .............................................................................................................................................20 

5.1. Comments on RSA/Legacy wind sensor comparison from Western Range Data.................................20 

References ........................................................................................................................................................... 21

Listof Acronyms ................................................................................................................................................ 22

4
List of Figures 

Figure 1. Schematic image of the propeller-and-vane type wind sensor used on the 5 ER towers listed 

in Table 1 (adapted from the R. M. Young Model 05305 Wind Monitor-AQ). See Computer 

Sciences Raytheon (2000) for details. Wind speed accuracy is +1- 0.58 kts. The starting 

thresholdwind speed is 0.64 kts............................................................................................................... 8 

Figure 2. Image of the ultrasonic type RSA wind sensor used on the 5 ER towers listed in Table 1 

(adapted from the Vaisala Model WS425 TJtrasonic Wind Sensor). See Vaisala (2004) for 

details. Wind speed accuracy is +1- 0.26 kts or 3% of wind speed, whichever is greater. The 

starting threshold is virtually zero............................................................................................................ 8 

Figure 3. Schematic of Legacy and RSA instrument configurations and wind-direction sectors used for 

wind speed comparisons on Tower 0313. Sector 1, spanning the SW from 135° to 315°, was 

used for comparing the Legacy 1 and the SW RSA sensor. Sector 2, spanning the NE from 

3150 to 1350, was used for comparing the Legacy2 and the SW RSA sensor. Wind direction 

from the Legacyl sensor was used as the reference............................................................................... 10 

Figure 4. (a) Sample size for average and (b) peak wind speed data from 29 Legacy sensors on 5 ER 

towers. The POR is 13 May-30 May 2005. Total sample size is 357,626........................................... 12 

Figure 5. (a) Average and (b) Peak wind speed comparisons for 17 sensor pairs on 4 ER towers. The 

POR is 13 May - 30 May 2005. Total sample size is 328,916. Each data point plotted had at 

least30 one-minute samples................................................................................................................... 13 

Figure 6. Average wind speed comparisons for each of the 19 LegacyfRSA sensors pairs on 5 ER 

towers. POR is 13 May - 30 May 2005. The legend indicates Legacy Tower ID, level (in ft) 

and Legacy sensor number, when applicable. Four outliers are marked by solid lines. Above 

-15 kts the number of samples becomes small (<30) for each sensor and the comparisons 

become noisy. The 1:1 solid diagonal line extends from the point 0,0 to the point 30,30, and 

represents the no-difference line............................................................................................................. 14 

Figure 7. UTC hour versus Peak Wind Speed (kts) from the RSA wind sensor at the 54 ft level on 

Tower0108............................................................................................................................................ 17

Figure 8. Peak Wind Direction versus Peak Wind Speed from the RSA wind sensor at the 054 ft level 

onTowerOl08......................................................................................................................................17 

Figure 9. Schematic horizontal cross-section of the relative orientation of ultrasonic transducer paths...............18 

Figure 10. (a) Average and (b) Peak wind speed comparisons for the best 15 RSA sensors on 5 ER 

towers. POR is 13 May - 30 May 2005. Total sample size is 171,726. Each data point 

plotted had at least 30 one-minute samples............................................................................................19 
List of Tables 

Table 1. Tower identification numbers (IDs) and sensor levels for RSA and Legacy wind data from the 

5 ER towers used in this study. Data from Legacy and RSA sensors were obtained at each level 

marked with the letters "L," "Li ," "L2," and "RSA," where "L" denotes one Legacy sensor 

and "LI," "L2," denotes two Legacy sensors at the same level...................................................................7 

Table 2. Legacy and RSA Tower IDs, number of levels with data, number of Legacy and RSA sensors 

at each level used in the comparison, and wind sectors used in sensor comparisons for 5 towers 

on the ER. See Figure 3 for a schematic depiction of the sectors on Legacy Tower 0313........................10 

Table 3. Sample size, in minutes, after the time series for each sensor pair was filtered by the wind 

direction sectors listed in Table 2. The Cross-Reference Number (CRN) will be used as a 

cross-reference to the RSA sensors. *TotaI sample size excludes CRNs 10 and 11 on Tower 

0108 (sample sizes in parentheses). See Section 4.2.4 for a detailed discussion of the RSA 

sensor data from Tower 0108....................................................................................................................11 

Table 4. Bias and standard deviation, in knots, of average wind speed for sensor-to-sensor comparisons. 

Entries in bold type were chosen for the composite best comparison....................................................... 15

Table 5. Bias and standard deviation, in degrees, of average wind direction for sensor-to-sensor 

comparisons. Entries m bold type were chosen for the composite best comparison.................................16
1. Introduction 

Launch Weather Officers, forecasters, and Range Safety analysts need to understand the performance of wind 

sensors at the Eastern (ER) and Western (WR) Ranges for weather warnings, watches, advisories, special ground 

processing operations, launch pad exposure forecasts, user Launch Commit Criteria (LCC) forecasts and 

evaluations, and toxic dispersion support. Through the Range Standardization and Automation (RSA) program, the 

current weather tower wind instruments are being switched from the Legacy propeller-and—vane (ER) and cup-andvane (WR) sensors to ultrasonic sensors. 

The Legacy sensors measure wind speed and direction mechanically, while the ultrasonic RSA sensors have no 

moving parts. Ultrasonic sensors, having no mechanical inertia, were originally developed to measure very light 

winds (Lewis and Dover 2004). The technology has evolved and now ultrasonic sensors provide reliable wind data 

over a broad range of wind speed. However, because ultrasonic sensors respond more quickly than mechanical 

sensors to the rapid fluctuations in speed that are characteristic of gusty wind conditions, comparisons of data from 

the two sensor types have shown differences in the statistics of peak wind speeds (Lewis and Dover 2004). The 45th 

Weather Squadron (45 WS) and the 30th Weather Squadron (30 WS) requested the Applied Meteorology Unit 

(AMU) to compare data from RSA and Legacy sensors to determine if there are significant differences between 

wind speed and direction information from the two systems. Short and Wheeler (2006) have documented a 

comparison of data from Legacy and RSA wind sensors on the WR. This report addresses the comparison of data 

from selected Legacy and RSA wind speed and direction sensors on the ER. 

2. Data and Sensor Description 

The 45 WS identified 5 ER towers to be used in the comparison of Legacy and RSA wind sensor data. Table I 

gives the Legacy tower numbers and sensor levels used in this study, with available data indicated by the letters "L" 

for Legacy and "RSA" for RSA. Data from 19 RSA sensors and 29 Legacy sensors were available. The Legacy and 

RSA wind sensors transmitted speed and direction readings every second to separate local processing systems. The 

local processing systems computed and recorded the following, based on the 1-second sensor readings. 

• One-minute average wind speed/direction, and 

• Peak wind speed/direction during the one-minute interval. 

The one-minute average wind speed/direction and the peak wind speed/direction data were used in this study. 

Table 1. Tower identification numbers (liDs) and sensor levels for RSA and Legacy wind 

data from the 5 ER towers used in this study. Data from Legacy and RSA sensors were 

obtained at each level marked with the letters "L," "LI," "L2," and "RSA," where "L" 

denotes one Legacy sensor and "LI ," "L2," denotes two Legacy sensors at the same level. 

Level

Tower ID Tower ID Tower ID Tower ID Tower ID 

(ft)

Legacy 0002 Legacy 0006 Legacy 0108 Legacy 0313 Legacy 0403 

RSA2 RSA6 RSA9 RSA16 RSA2O 

492 - - - LI,L2;RSA - 

394 - - - Ll,L2;RSA - 

295 - - - Li, L2; RSA - 

204 L; RSA Ll, L2; RSA - LI, L2; RSA - 

162 - - - Ll,L2;RSA - 

145 L;RSA - - - - 

090 L; RSA - - - - 

054 L; RSA Li, L2; RSA L; RSA Ll, L2; RSA L; RSA 

012 L; RSA Li, L2; RSA L; RSA Li, L2; RSA L; RSA
2.1. Legacy Wind Sensor 

Figure 1 shows a schematic image of the Legacy propeller-and-vane type wind sensor used on the 5 ER towers 

listed in Table 1. The Legacy wind sensor system is comprised of a wind vane that aligns itself with the wind 

direction and a propeller that spins at a rate directly proportional to the wind speed. The wind speed and direction 

information is output every second and a local data processing system determines the one-minute average and peak 

conditions. The 5 ER Towers used in the present study were among the 33 used by Case and Bauman (2004) for a 

nine-year climatological study of Legacy wind data from the Kennedy Space Center (KSC)/Cape Canaveral Air 

Force Station (CCAFS) tower network. 

Figure 1. Schematic image of the propeller-and-vane type wind sensor used on the 5 ER 

towers listed in Table I (adapted from the R. M. Young Model 05305 Wind Monitor-AQ). 

See Computer Sciences Raytheon (2000) for details. Wind speed accuracy is +1- 0.58 kts. The 

starting threshold wind speed is 0.64 kts. 

The one-minute average wind speed data from the Legacy sensors were recorded at approximately 1-knot 

intervals (0.0, 1.0, 1.9, 2.9, 4.1, 5.1, 6.0, 7.0, 8.0. 8.9, ...etc.). This sequence of values appears to have been first 

recorded to the nearest 0.5 ms 1 , then converted to knots, then recorded to the nearest 0.1 kts. The peak wind speed 

was recorded to the nearest knot and the average and peak wind directions were recorded to the nearest degree. 

2.2. RSA Wind Sensor 

Figure 2 shows an image of the Vaisala WS425 Ultrasonic Wind Sensor and its three equally spaced ultrasonic 

transducers mounted in a horizontal plane (Vaisala 2004). The sensor measures the time it takes for ultrasonic pulses 

to travel from one transducer to the other, in both directions. The transit time increases on upwind paths and 

decreases on downwind paths, the difference being proportional to the wind speed component along the path. Within 

every second 32 raw wind-speed estimates are derived along each of the three paths. A proprietary algorithm is used 

to quality-control the raw data and produce a I-second wind speed/direction reading. These 1-second data are used 

to produce a 1-minute average wind speed/direction reading and a peak wind speed/direction reading each minute. 

it 

Figure 2. Image of the ultrasonic type RSA wind sensor used on the 5 ER towers listed in 

Table I (adapted from the Vaisala Model WS425 Ultrasonic Wind Sensor). See Vaisala (2004) 

for details. Wind speed accuracy is ±1- 0.26 kts or 3% of wind speed, whichever is greater. The 

starting threshold is virtually zero.
The RSA average and peak wind speed data were recorded to the nearest 0.1 ms' (0.19 kts) and the average and 

peak wind direction data were recorded to the nearest degree. The RSA data was provided by Ms. Valek of 

Computer Sciences Raytheon. 

3. Analysis Procedure 

The analysis procedure was designed to compare Legacy and RSA sensor readings at the highest temporal 

resolution available and to avoid wind sheltering effects by the tower, when possible. This was accomplished by first 

matching times series minute-by-minute for all available sensors (Legacy, Legacyl and Legacy2, when available, 

and RSA) at each level on each tower. For towers having data from 2 Legacy sensors the Legacyl wind direction at 

each level on each tower was then used to separate the matched time series into two sectors. Each sector put the 

Legacy sensor on the upwind side of the tower for each of the two possible comparisons: 

. Sector 1: Legacy I versus RSA, 

. Sector 2: Legacy2 versus RSA. 

3.1. Extract Minute-by-Minute 

Time series of wind speed and direction were obtained for each Legacy sensor on each tower at each level. Data 

from one RSA sensor at each level on each tower was available for this study. The Legacy and RSA wind sensor 

data were matched, minute-by-minute. 

3.2. Wind Sector Filter 

The wind direction filter was based on the instrument mounting scheme for each tower and was designed to 

avoid effects of wind flow around the tower, when possible. This was done by restricting data for each Legacy 

sensor on Towers 0006 and 0313 to wind flow from the up-wind side of tower. Figure 3 shows a schematic of the 

mounting scheme for the Legacy and RSA sensors used on Tower 0313. Note that the Legacy and RSA sensors 

were mounted on opposite corners of the tower, southwest (SW) and northeast (NE). RSA sensors were mounted 

just inboard of the Legacy sensors, although data from only one RSA sensor was available for this study. RSA 

information indicated that the RSA 16 sensors were mounted on the SW side of Tower 0313. This mounting scheme 

was used for each level on Tower 0313. 

Figure 3 also defines 2 wind-direction sectors for Tower 0313. Data from Legacyl SW was used for 

comparison to the RSA sensor when the Legacyl SW sensor showed a wind direction between 1350 to 3150, 

clockwise. Otherwise, data from the Legacy2 NE sensor was used for comparison to the RSA sensor. 

The mounting scheme for Tower 0006 had Legacy and RSA sensors on the northwest (NW) and southeast (SE) 

sides of the tower. Wind direction sectors from 225° to 045° (NW; Legacyl), and 045° to 225° (SE; Legacy2) were 

used.
Legacy 

(S

SA Sensors 

315

Sector 2 

Legacy2 Sensor

(NE) 

Sector I

135 

Figure 3. Schematic of Legacy and RSA instrument configurations and wind-direction sectors used for wind 

speed comparisons on Tower 0313. Sector 1, spanning the SW from 135° to 315°, was used for comparing the 

Legacyl and the SW RSA sensor. Sector 2, spanning the NE from 315° to 135°, was used for comparing the 

Legacy2 and the SW RSA sensor. Wind direction from the Legacyl sensor was used as the reference. 

Table 2 shows tower ID numbers and wind direction sectors used to constrain the Legacy wind sensor data to 

the up-wind side of the tower.

Table 2. Legacy and RSA Tower IDs, number of levels with data, number of Legacy and RSA sensors at each level 

used in the comparison, and wind sectors used in sensor comparisons for 5 towers on the ER. See Figure 3 for a 

schematic depiction of the sectors on Legacy Tower 0313. 

Legacy Tower ID RSA Tower ID Levels with data Sensors Sector 1 Sector 2 

0403 20 2 L, RSA 0°—*360° N/A 

0313 16 7 L1,L2,RSA 135°-315° 315°—^135° 

0108 9 2 L, RSA 0°—*360° N/A 

0006 6 3 L1,L2,RSA 225°—*045° 045°—*225° 

0002 2 5 L, RSA 0° -* 3600 N/A

10 
Table 3 lists the sample size, in minutes, for each sector, and sensor pair, after filtering by wind direction. Total 

sample size excludes Legacy Tower 0108. See Section 4.2.4 for a detailed discussion of the RSA sensor data from 

Legacy Tower 0108. The Cross-Reference Number (CRN) will be used to simplif' further discussions. 

Table 3. Sample size, in minutes, after the time series for each sensor pair was filtered by the wind 

direction sectors listed in Table 2. The Cross-Reference Number (CRN) will be used as a cross-reference to 

the RSA sensors. *Total sample size excludes CRNs 10 and 11 on Tower 0108 (sample sizes in 

parentheses). See Section 4.2.4 for a detailed discussion of the RSA sensor data from Tower 0108. 

Cross-Reference 

N umber Legacy Tower ID Level 

(ft)

Sector 1 

Legacyl versus RSA

Sector 2 

Legacy2 versus RSA 

________________J

0403 054 18451 N/A 

2 j0403 012 14771 N/A 

3 0313 492 12245 7351 

4 0313 394 11905 7684 

5 0313 295 12709 7097 

6 0313 204 12802 5220 

7 0313 162 19824 19806 

8 0313 054 12828 6927 

9 0313 012 11962 7860 

10 0108 054 (12985) N/A 

11 0108 012 (15623) N/A 

12 0006 204 5173 13460 

13 0006 054 5056 13498 

14 0006 012 5091 12300 

15 0002 204 19088 N/A 

16 0002 145 19295 N/A 

17 0002 90 19280 N/A 

18 0002 054 19414 N/A 

19 0002 012 7921 N/A 

Total All Levels *227815 101203

Figure 4a shows how the total sample size from sectors 1 and 2 was distributed across Legacy average wind 

speeds. The average sample size has a plateau-like appearance from 5-to- 9 kts and falls to zero at 38 kts. The 

plateau results from a super-position of peaks from individual sensors. The distribution is right-skewed with a mean 

value of 7.44 kts, slightly to the right of the center of the plateau. 

Figure 4b shows how the total sample size from sectors I and 2 was distributed across Legacy peak wind 

speeds. The peak sample size has a single peak at 10 kts and a long tail of small sample sizes, with only one sample 

exceeding 45 kts. The distribution is right skewed, but has a mean value of 9.32 kts, slightly lower than the mode, 

due to large samples of low peak wind speeds.

EL 
Sample Size: Average Wind Speed 

Legacy Sensors: 5 Eastern Range Towers 

35000 

30000 

25000 

0

20000 

0

15000 

U) 10000 

5000 

0

0 5 10 15 20 25 30 35 40 

Legacy Average Wind Speed (kts)

Sample Size: Peak Wind Speed

Legacy sensors 5 Eastern Range Towers 

40000

b 

35000 

30000 

0

25000

. . 

20000 

U) . 

e

. 15000 

E

. . 

10000 

5000 • 

0 "rSUS.NM.1liUSSI*SSS 

0 5 10 15 20 25 30 35 40 45 50 

Legacy Peak Wind Speed (kts) 

a

. 

• •

• 

•

•

•

•••••,,.__ 

Figure 4. (a) Sample size for average and (b) peak wind speed data from 29 Legacy sensors on 5 ER towers. The 

POR is 13 May-30 May 2005. Total sample size is 357,626. 

4. Results 

The results of the sensor comparison are presented in this section in three different ways: 

• Overall composite results, 

• Sensor-by-sensor comparisons, and 

• Composite results from the most consistent sensors. 

The sensor-by-sensor comparisons were done for each LegacyIRSA pair. 

4.1. Overall Composite Results: Average and Peak Wind Speeds 

Data used for the overall composite results were obtained by first matching time series from all sensor pairs, 

minute-by-minute, and then excluding Legacy data from wind directions affected by the towers, as described in 

Section 3. A total of 329,018 one-minute comparisons of Legacy versus RSA wind information were obtained after 

the screening process. Total sample size excludes CRNs 10 and 11 on Tower 0108. See Section 4.2.4 for a detailed 

discussion of the RSA sensor data from Tower 0108. 

The overall comparison of all the screened data resulted in the following: 

• Overall Average Wind Speed: Legacy 7.72 kts, RSA 8.27 kts, RSA - Legacy = +0.55 kts 

• Overall Peak Wind Speed: Legacy 9.51 kts, RSA 10.72 kts, RSA - Legacy = + 1.21 kts 

Average wind speeds with sample sizes larger than 30 minutes during the POR ranged from 0 to 25 knots. Peak 

wind speeds with sample sizes larger than 30 minutes during the POR ranged from 1 to 28 knots 

In order to depict the difference between RSA and Legacy sensors over the full range of observed wind speeds, 

the AMU computed the overall results for 17 of the 19 RSA sensors, excluding Legacy Tower 0108, conditioned on 

the Legacy average and Legacy peak wind speeds. That is, for all Legacy one-minute average wind speeds of 1 knot 

at all levels on all towers, the corresponding RSA one-minute average wind speed was computed from data at all 

12 
levels on all towers. This procedure was followed for all Legacy average wind speeds, knot-by-knot, up to 25 knots. 

The results are plotted in Figure 5a. Above 25 knots the sample size for Legacy average wind speeds fell below 30 

one-minute-averages and the comparison results became noisy. Also, for all Legacy peak wind speeds of 1 knot, the 

corresponding average of all RSA peak speeds was computed. This procedure was followed for all Legacy peak 

wind speeds, knot-by-knot, up to 28 kts. The results are plotted in Figure 5b. At wind speeds above 28 knots the 

sample size for Legacy peak wind speeds fell below 30 and the comparison became noisy. 

Figure 5a shows RSA average wind speeds just above the 1:1 line with an offset of 0.64 kts when the Legacy 

speed is zero. This low wind speed performance is remarkably consistent with the starting thresholds for the two 

instruments: Legacy, 0.64 kts, RSA, essentially zero. Figure 5a also shows a weak inflection point near 15 kts. 

Figure Sb shows the RSA peak wind speeds are also above the 1:1 line with a weak inflection point near 17 kts. The 

inflections points are located in the region where the sample sizes for average and peak winds are falling rapidly, 

and the dispersion among individual sensors is increasing, as will be shown in the following section. 

Average Wind Speed Comparison

Legacy versus RSA: 4 Easterrn Range Towers 

35

a 

30 

25 

0,

20 

e 15 

C,

. 

<10

0 5 10 15 20 25 30 35

Legacy Average Wind Speed (kts)

Peak Wind Speed Comparison

Legacy versus RSA: 4 Eastern Range Towers 

35 

30 

25 

0) 0, 

(I)

15 

10 

5 

0

0 5 10 15 20 25 30 35

Legacy Peak Wind Speed (kts) 

../ 

F 

.7 

Figure 5. (a) Average and (b) Peak wind speed comparisons for 17 sensor pairs on 4 ER towers. The POR is 13 

May-30 May 2005. Total sample size is 328,916. Each data point plotted had at least 30 one-minute samples. 

4.2. Sensor-by-Sensor Comparisons 

The LegacyIRSA comparisons shown in Figure 5a and Figure Sb reveal the composite behavior of 17 of the 19 

RSA wind sensors with respect to 27 Legacy wind sensors for the one-minute average and peak wind speed data. A 

more detailed sensor-by-sensor comparison was also made to assess the consistency and reliability of the RSA 

sensors. 

4.2.1. Conditional Averages 

Figure 6 shows conditional averages of each of the 19 RSA sensors with respect to their collocated Legacy 

sensor. These were computed in the same manner as the curve shown in Figure 5a, with wind direction sectors as 

defined in Table 2. The majority of comparisons are tightly clustered just above the 1:1 line up to a speed of about 

15 kts. Above 15 kts the sample sizes for the individual sensors become smaller and the comparison become noisy. 

However, the data from 4 sensors are plotted with red, green and blue connecting lines to highlight variable 

deviations, even in the well sampled zone, above and below the 1:1 line. These 4 sensors were labeled as outliers in 

this initial comparison.

13
Average Wind Speed Comparison

Legacy versus RSA: 19 sensors on 5 ER Towers 

30

25 

5

x t3130122 

x t3130542 

x t313 1622 

x t3132042' 

x t3132952 

x t3133942 

x t3134922 

-o t002 012 

x t002 054 

x t002090 

x t002 145 

x t002204 

-e-t403 012 

x t403054 

x t0060121 

x t0060541 

x t006 204 1 

-t108 012 

-o--t108 054 

20 

"a 

C, 

C, 

Cl) 

"a

15 

C, 

a, 

C, 

>

10

rA 

0-v 

0 5 10 15 20 25 30

Legacy Average Wind Speed (kts) 

Figure 6. Average wind speed comparisons for each of the 19 Legacy/RSA sensors pairs on 5 ER towers. 

POR is 13 May - 30 May 2005. The legend indicates Legacy Tower ID, level (in ft) and Legacy sensor number, 

when applicable. Four outliers are marked by solid lines. Above -1 5 kts the number of samples becomes small 

(<30) for each sensor and the comparisons become noisy. The 1:1 solid diagonal line extends from the point 

0,0 to the point 30,30, and represents the no-difference line. 

4.2.2. Difference of Average Wind Speeds 

For each of the 19 RSA wind sensors on the 5 towers, the matched time series in Sectors 1 and 2 were used to 

compare overall average wind speeds between RSA-Legacy pairs. Table 4 lists the results. Bias was defined as the 

average of the RSA - Legacy difference in average wind speed. The standard deviation of the RSA - Legacy 

difference in average wind speed was also calculated and listed in Table 4.

14
Table 4. Bias and standard deviation, in knots, of average wind speed for sensor-to-sensor 

comparisons. Entries in bold type were chosen for the composite best comparison. 

CrossReference 

Number

Legacy 

Tower

Level 

(ft)

Sector 1 

RSA - Legacyl

Sector 2 

RSA - Legacy2 

1 0403 054 +0.16 +1- 0.92 N/A 

2 0403 012 +0.83+7-0.69 N/A 

3 0313 492 +0.77 +7- 1.62 +0.54 +/- 0.73 

4 0313 394 +1.12 +7- 2.06 +0.46 +1- 0.70 

5 0313 295 +0.78 +7- 1.50 +0.08 +1- 0.67 

6 0313 204 +0.9 1 +7- 1.78 +0.48 +/- 0.66 

7 0313 162 +0.96 +7- 1.55 +0.80 +/- 1.01 

8 0313 054 +0.60 +7- 1.40 +0.29 +1- 0.69 

9 0313 012 +0.29 +7- 0.79 +0.24 +1- 0.63 

10 0108 054 +0.31 +1- 1.86 N/A 

11 0108 012 +0.47+/-0.84 N/A 

12 0006 204 -0.15 +1- 0.69 +0.89 +1- 0.76 

13 0006 054 -0.05 +7- 0.72 +0.43 +1- 0.78 

14 0006 012 +0.27 +1- 0.78 +0.57 +1- 0.85 

15 0002 204 +0.80 +1- 0.93 N/A 

16 0002 145 +0.36+/-1.16 N/A 

17 0002 090 +0.41 +1- 0.95 N/A 

18 0002 054 +0.26+/-0.91 N/A 

19 0002 012 +0.98+7-3.35 N/A

From a technical point of view the small differences in average wind speeds reported by the Legacy and RSA 

sensors and listed in Table 4 are statistically significant, due to the large sample size and small standard deviation of 

differences in 1-minute wind speed between the sensors, +/- 0.90 kts. Under ideal conditions, with identical 

exposure the average wind speeds reported by the two instruments would be expected to be statistically 

indistinguishable. The small difference in average wind speed noted in this study, averaging < 0.5 kts for the most 

consistent sensor pairs, is not considered to be operationally significant. 

Under ideal conditions of identical exposure and high numerical precision in reported values, the standard 

deviation of differences in wind speed would be expected to be approximately +7- 0.64 kts, obtained by Pythagorean 

addition of the accuracies of the two sensors: +/- 0.58 kts (Legacy) and +1- 0.26 kts (RSA). Table 4 shows standard 

deviations somewhat larger than the theoretical value, likely attributable to sensor separation, small scale turbulence, 

and numerical truncation of reported values. The average observed standard deviation of +7- 0.90 kts is reasonable. 

Table 4 shows that for Legacy Tower 0313 the smallest bias and standard deviation were from Sector 2 (RSA - 

Legacy 2). Sector 2 utilizes the NE Legacy sensor, even though the corresponding RSA designation, Tower 16, 

would indicate the SW RSA sensor. On the other hand, for Legacy Tower 0006 the bias and standard deviation 

statistics are low for both Sector I and Sector 2, with Sector I being slightly better. This result is consistent with the 

understanding that the RSA Tower 6 sensor and the Legacyl Sensor are on the NW side of the tower. 

4.2.3. Difference of Average Wind Direction 

For each matched time series the average and standard deviation of direction differences were calculated. This 

procedure was followed for both sectors, when applicable, for each of 19 sensor levels on the 5 towers. The 

comparisons of wind direction differences are listed in Table 5.

15 
Table 5. Bias and standard deviation, in degrees, of average wind direction for sensor-to-sensor 

comparisons. Entries in bold type were chosen for the composite best comparison. 

CrossReference 

Number

Legacy 

Tower

Level 

(ft)

Sector I 

RSA - Legacyl

Sector 2 

RSA - Legacy2 

__________ 0403 054 -04.3+1-07.0 N/A 

2 0403 012 +49.9 +/- 07.6 N/A 

3 0313 492 -05.3 +1- 05.4 +05.4 +1- 04.9 

4 0313 394 -05.9 +1- 06.9 -02.8 +1- 06.0 

5 0313 295 -06.8 +1- 04.4 +09.1 +1- 05.7 

6 0313 204 -05.9 +/- 04.8 -10.1 +1- 04.1 

7 0313 162 -01.5 +1- 08.0 -03.0 +1- 04.8 

8 0313 054 -01.6 +/- 05.9 +00.0 +1- 07.3 

9 0313 012 -04.6 +/- 06.6 -00.2 +1- 09.6 

10 0108 054 -03.6 +/-26.8 N/A 

11 [012 +04.2+!- 11.1 N/A 

12 0006 204 -01.4 +/- 04.1 +0.6 +/- 04.6 

13 0006 054 -03.6 +/- 06.2 +04.7 +/- 04.9 

14 0006 012 -02.6 +1- 11.4 +04.4 +/- 09.1 

15 0002 204 -01.9 +1-03.7 N/A 

16 0002 145 +06.6+/-04.3 N/A 

17 0002 090 03.6 +1- 04.3 N/A 

18 0002 054 +03.4+/-04.7 N/A 

19 0002 012 +01.1+/-11.8 N/A

The largest bias in wind direction shown in Table 5 is + 49.9° for CRN 2, at the 012 ft level on Legacy Tower 

0403. This large bias value suggests a misaligned sensor. The largest standard deviation in wind direction shown in 

Table 5 is 26.8° for CRN 10, at the 054 ft level on Legacy Tower 0108. Both RSA sensors on Legacy Tower 0108 

were classified as outliers on the basis of patterns in the average wind speed comparisons shown in Figure 6. The 

following section describes anomalous peak wind speeds from the RSA sensor at the 054 ft level on Legacy Tower 

0108.

4.2.4. Anomalous Peak Wind Speeds from RSA Sensors on Tower 0108 

This section describes an extreme example of anomalous peak wind speeds affecting 4 % of the data from the 

RSA sensor at the 54 ft level on Tower 0108. Table 5 shows that the average wind direction data from this sensor 

(CRN 10) showed the largest overall variability from collocated Legacy sensor data; a standard deviation of 26.8°. 

Further examination of data from this sensor showed anomalous peak wind speeds, documented below. 

Figure 7 shows the diurnal cycle of peak wind speeds from the RSA sensor at the 54 ft level on Tower 0108. 

The RSA sensor data stream included 4 quality flags with each one-minute report. All data points plotted in Figure 7 

had all 4 quality flags set at zero, indicating "nominal." However, there is a clear separation between the cluster of 

reasonable looking values < 40 kts and a higher cluster > 100 kts. The higher cluster is considered anomalous, 

because the highest peak wind speed observed by the collocated Legacy wind speed sensor during the POR was 27 

kts. Note the absence of anomalous data from Universal Coordinated Time (UTC) hours 15 through 20 

One unresolved puzzle concerning the anomalous wind speeds is that the measurement range for the ultrasonic 

anemometer is given as 65 rn/s (125 kts; Vaisala 2004), yet values as high as 150 kts were archived.

16 
Diurnal Cycle iii RSA Peak Wind Speed from Ultrasonic Auienuneter 

ER Towei 108: 54ft level 

13-30 May. 2005 

1601 

140 

120 

4) 4)

80 

60 

4,

20 

U

0 4 8 12 16 20 24 

UTC Hour 

Figure 7. UTC hour versus Peak Wind Speed (kts) from the RSA wind sensor at the 54 ft level on Tower 0108. 

Figure 8 shows the directional dependence of peak wind speed from the RSA sensor at the 54 ft level on Tower 

0108. The anomalous peak wind speeds are clustered at 5 directions; 300, 150°, 210°, 270° and 330°. 

Direction of RSA Peak Wind Speed from Ultrasonic Anemometer 

ER Tower 108: 5411 level 

13-30 May 2005 

160 - 

140 

120 

100 

4, __________________________ 

80 _____ 

60 _______ ___ 

4) 40 ____ _______ 

20 

0

0 30 80 90 120 150 180 210 240 270 300 330 360 

Peak Wimid Dii ection 

I_ - --- 

I __ _ 

i• __I 

c I "

— .. - - . - — - ....A...a..._. - 

Figure 8. Peak Wind Direction versus Peak Wind Speed from the RSA wind sensor at the 054 ft level on Tower 

0108. 

The 60° separation between the anomalous peak wind speed clusters shown in Figure 8 appears to be related to 

the geometric layout of the sensor as follows:

B.

. $ 

*

*

4 S

4 

• • 

. 

$

.5 4 

I

•

S $ 

* $ S• 

• 

•

. I 

,•.t • 

O

I

•*

17 
Figure 9 shows a schematic horizontal cross-section of the triad of ultrasonic transducers that comprise the 

ultrasonic wind sensor. The instrument configuration is that of an equilateral triangle, resulting in 3 equal baselines, 

—15 cm long, with a transducer on each end. 

Schematic Horizontal Cross-section of the

Relative Orientation of Ultrasonic Transducer Paths 

© - Transducer N 0300 

3300

. 

W ---- E 

270°

• >

090° 

210° 150° 

S 

-0.5

0

Figure 9. Schematic horizontal cross-section of the relative orientation of ultrasonic transducer paths. 

Note that the transducer paths shown in Figure 9 are aligned at 600 intervals from each other. The occurrence of 

anomalously high peak wind speeds at 60° intervals strongly suggests they are related to the geometry of the 

instrument. 

One hypothesis for the occurrence of anomalous wind speeds at 60° intervals is the effect of one transducer 

being blocked. This would leave only one transducer pair with the capability of inferring a wind speed/direction 

along their connecting path. This hypothesis could be tested in a controlled environment. Candidates for such 

blockage in the field would be birds, bats, or insects. It is also possible that the occurrence of anomalously high peak 

wind speeds is an indicator for a certain mode of instrument failure, influenced by the diurnal cycle of temperature 

and humidity, since the span of daytime hours from 14-to-20 UTC were free of the anomalies.

18 
4.3. Best Composite Results: Average and Peak Wind Speeds 

The 15 RSA sensors that showed the most consistent performance, with respect to the Legacy sensors, can be 

inferred from Table 4 and Table 5 by including all RSA sensors with speed/directional differences in bold type. 

These 15 RSA sensors were used to produce composite comparisons, following the procedure described in Section 

4.1. The results for average wind speed are shown in Figure 1 Oa and the results for peak wind speed are shown in 

Figure lob.

Average Wind Speed Comparison

Legacy versus RSA: 5 Easterrn Range Towers

15 Best Sensors 

35

a 

30 

25 

20 

C

tTt ,15 

10 

U)

0 5 10 15 20 25 30 35

Legacy Average Wind Speed (kts)

Peak Wind Speed Comparison 

Legacy versus RSA: 5 Eastern Range Towers 

15 Best Sensors 

35 

30 

25 

a 

a

20 

'V

15 

10 

5 

0

0 5 10 15 20 25 30 35

Legacy Peak Wind Speed (kts) 

b • 

. 

. 

. 

. ./ . ,,/ ./ 

9 

Figure 10. (a) Average and (b) Peak wind speed comparisons for the best 15 RSA sensors on 5 ER towers. 

POR is 13 May - 30 May 2005. Total sample size is 171,726. Each data point plotted had at least 30 oneminute samples. 

Figure 1 Oa shows the best 15 RSA average wind speeds just above the 1:1 line. Figure lOb shows the best 15 

RSA peak wind speeds are also above the 1:1 line with a weak inflection point near 17 kts. 

Comparisons of the 15 sensor composite were slightly different than the overall comparison cited in Section 4.1. 

• Composite Average Speed: Legacy 08.09 kts, RSA 08.47 kts, RSA - Legacy = + 0.38 kts 

• Composite Peak Speed: Legacy 09.79 kts, RSA 10.73 kts, RSA - Legacy = + 0.94 kts 

The differences in peak wind speeds reported by the Legacy and RSA sensors are statistically significant, due to 

the large sample size and relatively small standard deviation of differences in peak wind speed between the sensors, 

+1- 1.10 kts. The differences in peak wind speeds are also consistent with previous studies and are physically 

reasonable, given the nature of the sensors. The difference in peak wind speed noted in this study, averaging 0.94 

kts for the most consistent sensor pairs, indicates that the change from mechanical to ultrasonic wind sensors has the 

potential to increase reported peak wind speeds, which could result in a small decrease in launch availability, 

depending on the LCC threshold. 

Consider a hypothetical LCC threshold of 20 kts. Based on the sample of wind conditions used in this study, the 

probability of peak wind speeds at 20 kts or less using the Legacy data was 95.2%. For the same 20 kt threshold the 

RSA data showed a probability of 92.3%. That represents a 3% decrease in launch availability for the hypothetical 

threshold.

19
5. Conclusions 

The RSA program is changing wind-measurement instrumentation on wind towers from the current Legacy 

mechanical systems to an RSA ultrasonic system with no moving parts. Launch Weather Officers, forecasters and 

Range Safety analysts need to understand the performance of the new RSA sensors and possible impacts on weather 

warnings, watches, advisories, special ground processing operations, launch pad exposure forecasts, user LCC 

forecasts and evaluations, and toxic dispersion support. This AMU report addresses the comparison of selected 

Legacy and RSA wind speed and direction sensors on the ER. 

Data from 29 Legacy and 19 RSA wind sensors on 5 ER towers was obtained and analyzed by the AMU to 

characterize differences in average wind speed, peak wind speed and wind direction. The Legacy system on the ER 

uses a vane to measure wind direction and a spinning propeller to measure wind speed. The RSA system relies on 

the effect of wind on the transit time of ultrasonic pulse between closely-spaced transducers in a triangular array. 

A total of 357,626 one-minute data samples, from the 18-day interval 13 May to 30 May 2005, were compared. 

Sensor heights ranged from 12 to 492 ft. Data were obtained from I RSA and 1 or 2 Legacy sensors at each level, 

depending on the tower. For towers with 2 Legacy sensors, an initial screening process was used to select Legacy 

sensor data from the upwind side of those towers for use in the comparisons. 

A secondary screening identified anomalous RSA peak wind speed readings at Tower 0108 and data from 2 

RSA sensors on that tower were analyzed separately. 

The comparison of 329,018 minutes of secondary screened data from 17 RSA sensors resulted in:the following: 

. Overall Average Wind Speed: Legacy 7.72 kts, RSA 8.27 kts, RSA - Legacy = + 0.55 kts 

. Overall Peak Wind Speed: Legacy 9.51 kts, RSA 10.72 kts, RSA - Legacy = + 1.21 kts 

The AMU used the Legacy wind data as a "reference" and identified 15 RSA sensors with the closest 

agreement, based on differences in speed and direction. The 15 RSA sensors were used to define a composite 

average-LegacyfRSA comparison and the peak wind speed data from the same 15 RSA sensors were used to define 

a composite peak-Legacy/RSA wind speed comparison. 

Comparisons of the 15 sensor composite were slightly different than the overall comparison cited above. 

• Composite Average Speed: Legacy 08.09 kts, RSA 08.47 kts, RSA - Legacy = + 0.38 kts 

• Composite Peak Speed: Legacy 09.79 kts, RSA 10.73 kts, RSA - Legacy = + 0.94 kts 

The positive bias in the composite RSA average wind speed was roughly constant over the range 0-to-25 kts. 

The positive bias in the composite RSA peak wind speed ranged from 0.44 kts to 1.14 kts over the range 1 -to-28 kts. 

From a technical point of view the small differences in average wind speeds reported by the Legacy and RSA 

sensors are statistically significant, due to the large sample size and small standard deviation of differences in 1-

minute wind speed between the sensors, +1- 0.90 kts. From a practical point of view the differences in peak wind 

speeds are more important, indicating that the change to ultrasonic sensors can be expected to result in a small 

increase in reported peak wind speeds. An increase in peak wind speeds would result in a decrease of launch 

availability, depending on the LCC threshold wind speed. For example, the probability of peak wind speeds at 20 kts 

or less using the Legacy data was 95.2%. For the same 20 kt threshold the RSA data showed a probability of 92.3% 

5.1. Comments on RSAILegacy wind sensor comparison from Western Range Data 

Short and Wheeler (2006) documented a similar comparison of RSA and Legacy wind sensor data from 5 

towers on the WR. Overall, the WR and ER comparisons are consistent. The average RSA wind speed was about 

0.35 kts higher than the average Legacy wind speed. The peak RSA wind speed averaged about 1 kt higher than the 

peak Legacy wind speed with a tendency for an increasing difference with increasing wind speed. 

One significant difference between the ER and WR studies was the presence of anomalously high peak wind 

speeds from one ER RSA sensor. The anomalous peak wind directions were clustered at 60° intervals and the 

anomalous peaks were absent in the afternoon, suggesting either interference from wildlife (birds, bats, insects) or 

the signature of a failure mode of the instrument influenced by the diurnal cycle in temperature and humidity. 

Because the WR data were restricted to the afternoon hours, it may be prudent to examine some night-time or 

early morning data to determine if similar anomalous behavior is detected.

20
References 

Case, J, L., and W. H. Bauman, III, 2004: Tower Mesonetwork Climatology and Interactive Display Tool. NASA 

Contractor Report CR-2004-21 1526, Kennedy Space Center, FL, 88 pp. [Available from ENSCO, Inc., 1980 N. 

Atlantic Ave., Suite 230, Cocoa Beach, FL, 32931.] 

Computer Sciences Raytheon (CSR), 2000: 45th Space Wing Eastern Range Instrumentation Handbook, Computer 

Sciences Raytheon, Inc., 758 pp. 

Lewis, R., and J. M. Dover, 2004: Field and Operational Tests of a Sonic Anemometer for the Automated Observing 

System. AMS Eighth Symposium on Integrated Observing and Assimilation Systems for Atmosphere, Oceans, 

and Land Surface. Seattle, WA, 12-16 January 2004. Paper 7.1, 6 pp. 

Short, D.A., and M. W. Wheeler, 2006. RSAILegacy Wind Sensor Comparison: Part I: Western Range. NASA 

Contractor Report CR-2006-2 14200, Kennedy Space Center, FL, 23 pp. [Available from ENSCO, Inc., 1980 N. 

Atlantic Ave., Suite 230, Cocoa Beach, FL, 32931.1 

Vaisala, 2004: Ultrasonic Wind Sensors WS425 User's Guide. Vaisala Oyj, Helsinki, Finland, 95 pp.

21
List of Acronyms 

30 WS 30th Weather Squadron 

45 WS 45th Weather Squadron

AMU Applied Meteorology Unit 

CCAFS Cape Canaveral Air Force Station 

CSR Computer Sciences Raytheon 

CRN Cross-Reference Number 

ER Eastern Range 

ID Identification Number 

KSC Kennedy Space Center 

LCC Launch Commit Critena 

NE Northeast 

NW Northwest 

POR Period of Record 

RSA Range Standardization and Automation 

SE Southeast 

SW Southwest 

UTC Universal Coordinated Time 

WR Western Range

22 
NOTICE 

Mention of a copyrighted, trademarked or proprietary product, service, or document does not constitute 

endorsement thereof by the author, ENSCO Inc., the AMIU, the National Aeronautics and Space Administration, or 

the United States Government. Any such mention is solely for the purpose of fully informing the reader of the 

resources used to conduct the work reported herein.

23

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1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE

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3. DATES COVERED (From - To) 

17-05-2006 Final June 2005 - May 2006 

4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER 

RSA/Legacy Wind Sensor Comparison: Part II: Eastern Range NAS1O-01052 

5b. GRANT NUMBER 

5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 5d. PROJECT NUMBER 

David Short ________________________________________ 

Mark Wheeler 5e. TASK NUMBER 

5f. WORK UNIT NUMBER 

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ENSCO Inc. REPORT NUMBER 

1980 N. Atlantic Ave Suite 230 06-004 

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NASA/CR-2006-2 14205 

12. DISTRIBUTION/AVAILABILITY STATEMENT 

Unclassified, Unlimited 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

This report describes a comparison of data from ultrasonic and propeller-and-vane anemometers on 5 wind towers at Kennedy 

Space Center and Cape Canaveral Air Force Station. The ultrasonic sensors are scheduled to replace the Legacy propeller-and-vane 

sensors under the Range Standardization and Automation (RSA) program. Because previous studies have noted differences 

between peak wind speeds reported by mechanical and ultrasonic wind sensors, the latter having no moving parts, the 30th and 

45th Weather Squadrons wanted to understand possible differences between the two sensor types. The period-of-record was 13-30 

May 2005, A total of 357,626 readings of 1-minute average and peak wind speed/direction from each sensor type were used. 

Statistics of differences in speed and direction were used to identif' 15 out of 19 RSA sensors having the most consistent 

performance, with respect to the Legacy sensors. RSA average wind speed data from these 15 showed a small positive bias of 0.38 

kts. A slightly larger positive bias of 0.94 kts was found in the RSA peak wind speed. 

15. SUBJECT TERMS 

Peak Wind Speed, Ultrasonic Anemometer, Propeller-and-Vane Anemometer, Instrument Comparison 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT b. ABSTRACT PAGES Dr. Francis J. Merceret c. THIS PAGE

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