In recent years, there has been an increased availability of different types of remote sensors for measuring atmospheric parameters. With the introduction of remote sensors into field operation, questions have arisen as to their accuracy and precision. An attempt was made to address this issue by analyzing and intercomparing sets of wind and temperature data obtained during the Joint Acoustic Propagation Experiment (JAPE-9l) conducted at White Sands Missile Range, New Mexico, in Jul. and Aug. 1991. The remote sensing systems that were deployed included a 924 MHz wind profiler, two Doppler acoustic sodars, and a Radio Acoustic Sounding System (RASS). In situ measurements of wind, temperature, and humidity were also obtained from radiosondes. Individual system characteristics and the results of intercomparing the derived wind and temperature data from each of the systems are presented

Cook, Greg J.

Okrasinski, Richard J.

Olsen, Robert O.

English

NASA Technical Reports Server

/ y4jo/
N94-2<2 0
INq'ERCOMPARISON OF REMOTE AND BALLOON-BORNE
SENSORS OPERATED AT JAPE-91
Richard J. Okrasinski and Greg J. Cook
Physical Science Laboratory
New Mexico State University
Las Cruces, NM
f
7 5
Robert O. Olsen
U.S. Army Research Laboratory
Battlefield Environment Directorate
White Sands Missile Range, NM
SUMMARY
In recent years, there has been an increased availability of different types of remote sensors
for measuring atmospheric parameters. With the introduction of remote sensors into field operation,
questions arise as to their accuracy and precision. An attempt was made to address this issue by
analyzing and intercomparing sets of wind and temperature data obtained during the Joint Acoustic
Propagation Experiment (JAPE-91) conducted at White Sands Missile Range, New Mexico, in July
and August, 1991. The remote sensing systems that were deployed included a 924 MHz wind
profiler, two Doppler acoustic sodars, and a Radio Acoustic Sounding System (RASS). In situ
measurements of wind, temperature, and humidity were also obtained from radiosondes. Individual
system characteristics and the results of intercomparing the derived wind and temperature data from
each of the systems are presented.
INTRODUCTION
The Joint Acoustic Propagation Experiment (JAPE-91) was conducted at White Sands Missile
Range in south central New Mexico during July 11 - 28 and August 19 - 29, 1991. Two Doppler
sodars, a 924 MHz wind profiler, and a Radio Acoustic Sounding System (RASS) were deployed
by the U.S. Army Research Laboratory to collect boundary-layer wind and temperature data in
support of the experiment. Upper-air wind, temperature, and humidity data were also collected by
periodically released rawinsondes.
This information was later analyzed to evaluate the capabilities of the four remote sensors.
Wind data from the UHF profiler and temperature data collected by the RASS were statistically
compared with concurrent rawinsonde measurements. Similarly, simultaneous measurements from
the two sodars were compared with each other and with concurrent wind profiler data. The percent
31
https://ntrs.nasa.gov/search.jsp?R=19940019737 2020-06-16T17:02:05+00:00Z
of time that datawere successfullymeasuredat eachsamplingheightwasalso calculatedto determine
the functional vertical rangeof eachsensor.
INSTRUMENTDESCRIPTION
Both sodars, manufactured by REMTECH, Inc., transmit one vertical and two tilted acoustic
beams. Changes in the acoustic refractive index caused by temperature fluctuations scatter some of
the transmitted energy back to the antennas. Doppler shifts in these backscattered signals are used
to derive the wind velocities along the three beam paths from which horizontal wind speeds and
directions are then computed. The sodars are used to measure winds between 50 and 750 m above
the surface.
The older A0 model uses a trailer-mounted array of three acoustic antennas, two of which are
tilted 18 ° from the vertical, and the newer PA2 uses a single phased array antenna with three
electronically steered beams, two of which are directed 30 ° from the vertical and 90 ° from each
other. Frequency coded transmissions are propagated at frequencies centered at 1600 Hz with an
acoustic power of 60 W by the A0 and at 2100 Hz with an acoustic power of 140 W by the PA2.
The wind profiler transmits three 924 MHz beams, one vertical and two tilted 15° from
vertical, from three antennas. Doppler shifts in the backscattered signals are used to derive the
wind velocities along the beam paths. One-hour-averaged horizontal wind data are computed from
the radial velocities using a random sample consensus technique. The maximum measurement
height is a function of the intensity of the backscattering and the vertical resolution of the wind
data, but is usually between 2 and 4 km. Peak pulse power is 500 W.
The vertical radar antenna is also used to track 2000 Hz acoustic beams transmitted by the
conjunctive R.ASS. Doppler shifts in the backscattered energy determine the speed of the acoustic
signal, which is proportional to the virtual temperature of the medium. Maximum measurement
height is about 1 km. Both the wind profiler and the R.ASS were developed by the NOAA Wave
Propagation Laboratory.
Different radiosonde systems were deployed for the July and August phases of JAPE. In July,
a system manufactured by Atmospheric Instrument Research, Inc. (AIR) was used, which consists
of a 1680 MHz sonde tracked by an automatic radio theodolite using a phase array antenna.
Height, temperature, humidity, and balloon-to-ground azimuth and elevation angles were recorded
for every 4 - 5 seconds of flight. In August, an O_ega Navaid system, using equipment
manufactured by Vaisala Oy, was substituted to collect data at greater heights. Vaisala RS-80
radiosondes tracked by a Vaisala Digicora ground station provided measurements for every 10
seconds of flight.
32
DATA COLLECTION
JAPE-91wasconductedin the extreme southeast comer of White Sands Missile Range in
south central New Mexico. This is an arid region situated in a broad basin between two mountain
ranges. The nearest significant feature is the 300-m high Jarilla Mountains approximately 4 km to
the east. The test area slopes from an elevation of 1275 to 1254 m above sea level from south to
north.
The A0 sodar, the wind profiler and RASS, and the radiosonde station were located at the
same site. The PA2 sodar was situated approximately 4.5 km south, next to a 40-m hill. Other
than the hill, there were no significant terrain features in the vicinity of the two locations.
Fifteen-minute-averaged wind data were collected by the PA2 sodar during July 21 - 29 every
50 m from 50 to 750 m. Concurrent A0 winds were measured every 50 m from 50 to 750 m from
2045 on July 20 to 1515 on July 27 MDT, and from 50 to 600 m the rest of the time. Both sodars
were operated more than 90% of the time between midnight July 21 and 0930 on July 29 MDT.
Only the A0 was operated in August.
Two sets of one-hour-averaged UHF wind profiler data were collected. Winds with a vertical
resolution of 101 m were measured at 25 levels between 167 and 2601 m, and 203-m resolution
winds were measured at 24 levels between 246 and 4911 m. The profiler was turned off during
several testing periods to avoid interfering with other instrumentation. A total of 84 hours of data
were collected in July.
Five-minute-averaged virtual temperatures were collected hourly by the RASS between 127
and 1283 m above the ground at 12 equally spaced heights. Forty-five hours of data were collected
in July and 144 hours were collected in August.
Thirty-three AIR radiosondes were flown during July and tracked to 5 km above the surface.
Seven Vaisala sondes, tracked to 15 - 20 km, were released during August.
DATA COMPARISONS
UHF Wind Profiler
In most cases, the wind profiler does not successfully collect data at all of its programmed
altitudes. The strength of the returned signal is a function of the intensity of the turbulent
scattering in the region being probed and is often too weak to be interpreted. Lower resolution
winds are measured with greater success, because longer pulse lengths and more energy are
transmitted. The profiler height range, therefore, is dependent on both the state of the atmosphere
and the resolution of the measurement. The percent of time that one-hour wind profiler measurements
were successfully collected in July was computed for each interrogation height and plotted in
33
Figure 1. Considerablymore low-resolutiondatawere obtained. At 2 km, for example, 101-m
and 203-m resolution winds were collected about 55% and 90% of the time, respectively.
To investigate the accuracy of these measurements, low-resolution (203-m) wind profiler data
collected in July were statistically compared with data from 20 rawinsonde soundings that were
launched within 30 minutes of one of the profiler interrogation times. The rawinsonde winds were
calculated for 200-m layers and interpolated to the profiler heights, so that both data sets had
approximately the same vertical scale. There is still a rather large temporal difference, however,
because the profiler winds were averaged over one hour and the rawinsonde winds were computed
for approximately 40 seconds of flight. In addition, the balloon drifts away from the site as it
rises. Nevertheless, the agreement between the rawinsondes and profiler was fairly good, as
shown in Figure 2, where the rms wind speed and vector wind differences are plotted versus
height. The latter were calculated by taking the square root of the sum of the mean square
differences in the east-west and north-south component winds and are, therefore, a function of the
differences in both wind speed and direction. Most of the rms vector differences were close to
2.5 m s4. This is not much larger than the 1.5 - 2.0 m s4 vector differences that were found
between the same radiosonde system and a reference high-precision radar during a radiosonde
intercomparison experiment (ref. 1). These statistics also compare favorably with the results of
another study (ref. 2) in which the standard deviation of the differences in the east-west and north-
south wind velocities measured by a wind profiler and rawinsondes were found to be about 2.5 m s 4.
101M 203M WSPD .... VECT
5 5
m
4
22
1
0
0 20 40 60 80 1O0
DATA
Figure 1. Percent of time wind data were
successfully collected by the UHF wind
profiler at 101-m (solid line) and 203-m
(dashed line) resolutions.
34
4"..
1___2 -
5
<
1-
0
0
,p_,o
lit illltUliUnlltili
1 2 3
RMS DIFF. (M S -1)
4
Figure 2. Rms wind speed differences (solid
line) and vector wind differences (dashed line)
of concurrent UHF wind profiler and
rawinsonde data.
Sodars
Because the strength of the backscattered sodar signal is largely a function of the intensity and
scale of the temperature fluctuations in the region being probed, the sodar height ranges vary
greatly with atmospheric conditions. Using 15-minute-averaged wind data collected by the A0 and
PA2 sodars between July 21 - 29, the success rate of data collection was computed as a function of
altitude and is shown in Figure 3. The PA2, as expected, had a greater range. At 600 m, for
example, the A0 and PA2 sodars obtained a measurement approximately 40% and 85% of the time,
respectively.
Using this same data set, the comparability of the two sensors was studied by calculating
statistics of the differences between their simultaneous measurements. The number of concurrent
data points ranged from 616 at 100 m to 300 at 600 m. The rms wind speed and vector wind
differences, plotted in Figure 4, were close to 2 and 3 m s_, respectively, at all altitudes. Means
and standard deviations of the differences in wind speed and direction, shown in Figure 5, were
also calculated for comparison with the results of an earlier analysis of 20-minute-averaged wind
data collected by two collocated A0 sodars (ref. 3). The mean differences found in that study are
comparable in magnitude to the JAPE statistics, but their wind speed and direction standard
deviations of 1.1-1.4 m s_ and 22 - 32 °, respectively, are somewhat smaller. The poorer JAPE
statistics may be partially due to the 4.5 km separation of the two sodars.
600
500
_E 400-
L_
C3 300-
I--
l--
--J 200-
.<
100 --
AO PA2
I
I
f
0 I I J I J I 1 I I
0 20 40 60 80 100
DATA
Figure 3. Percent of time horizontal wind data
were successfully collected by the A0 (solid
line) and PA2 (dashed line) sodar.
600
m
500 --
400
k,"
200
<
100 -
WSPD .... VECT
0 illllJllt lit illlll _
0 1 2 3 4
RMS DIFF. (M S-')
Figure 4. Rms wind speed differences (solid
line) and vector wind differences (dashed line)
of concurrent A0 and PA2 sodar wind data.
35
M EAN STDV MFAN STDV
600 600
500
400
!,1
£3 300
2
200
<
1DO
0
500
(
llllllilllllli
-2 -1 0
WIND
'_ 400
LIJ
30O
2
5 200
<
1O0
0 ,
-90
JlJlllJlllllJl I I I I I I J J I I I I I I I
--3 1 2 3 --60 --30 0 30 60 90
SPEED (M S-') WIND DIR. (DEG)
Figure 5. Means (solid lines) and standard deviations (dashed lines) of the differences in concurrent
A0 and PA2 sodar wind speeds and directions.
A similar comparison of concurrent sodar and wind profiler measurements was also conducted.
The social" data were first averaged over one-hour periods and vertically interpolated to the profiler
heights. Statistics of the differences between simultaneous one-hour sodar and profiler data were
then calculated using only those periods when data were available from all three sensors. The rms
wind speed and vector wind differences are shown in Table I. The A0 sodar, which was at the
same site as the wind profiler, was found to be in better agreement with the profiler than the more
distant PA2.
Radio Acoustic Sounding System (RASS)
The height range of the R.ASS, which consists'of a sodar and a radar, also varies with
atmospheric conditions. The data collection success rate, calculated with measurements from both
the July and August phases of JAPE, is shown in Figure 6. Almost no data were obtained above
652 m. Measurements up to this level were statistically compared with virtual temperatures
computed from 22 radiosonde soundings, which were released within 30 minutes of one of the
RASS interrogation times. Means, standard deviations, and root-mean-squares of the differences
are printed in Table II. The rms differences of .7 - .9 °C are comparable with those found in an
earlier study (ref. 4).
36
TableI. Sodar-UHFProfiler RmsDifferences
ALT WIND SPEED VECTOR WIND
A0-UHF PA2-UHF A0-UHF PA2-UHF
(m) (m s"l) (m s"l)
NPTS
268 1.5 2.0 1.9 2.5
369 1.5 2.0 1.9 2.5
471 1.4 1.9 1.7 2.5
25
15
13
1500 t
'_'1000
2
_' 500
<
I ' l I i I i I l
0 20 40 60 80 1O0
DATA
--:-;0
Figure 6. Percent of time temperature data were successfully collected by the RASS.
37
Table 17. R.ASS-Radiosonde Differences in Virtual Temperature
ALT MEAN SDEV RMS NPTS
(m) (°C)
233 .0 .7 .7 20
338 .3 .7 .8 22
442 .6 .7 .9 21
548 .5 .6 .8 17
652 .4 .7 .8 12
CONCLUSIONS
-z
Statistical agreement between the radiosonde data and the wind profiler and R.ASS meas-
urements collected at JAPE was comparable with the results of other similar studies. The rms
temperature and vector wind differences between concurrent measurements were approximately
.8 °C and 2.5 m s l, respectively. Standard deviations of the differences in the sodar wind speeds
and directions, however, were somewhat greater than those that were found between two collocated
sodars in a previous study. This may be partially due to the 4.5 km separation of the two sensors.
The sodar rms vector wind differences were about 3 m sl.
Data were successfully collected at least 50% of the time at all heights below 600 m by the
A0 sodar, below 652 m by the RASS, and below 2.3 and 4.3 km by the UHF wind profiler at
101-m and 203-m vertical resolutions, respectively. More than 85% of the PA2 data were collected
at all altitudes up to 600 m.
REFERENCES
, Olsen, R. O.; Okrasinski, R. J.; and Schmidlin, F. J.: Intercomparison of Upper Air Data
Derived from Various Radiosonde Systems. In Preprints: 7th Syrup. on Meteor.
Observations and lnstrumentation, Amer. Meteor. Sot., Jan. 1991, pp. 232-236.
, Weber, B. LI; and Wuertz, D. B.: Comparison of Rawinsonde and Wind Profiler Radar
Measurements. J. Atmos. Oceanic TechnoL, vol. 7, no. 1, Feb. 1990, pp. 157-174.
. Chintawongvanich, P.; Olsen, R. O.; and Biltott, C. A.: Intercomparison of Wind
Measurements from Two Acoustic Doppler Sodars, a Laser Doppler Lidar, and In Situ
Sensors. J. Atmos. Oceanic TechnoL, vol. 6, no. 5, Oct. 1989, pp. 785-797.
38
4. May, P.T.; Moran, K. P.; and Strauch,R. G.: TheAccuracyof RASSTemperature
Measurements..]Appl.Meteor., vol. 28, no. 12, Dec. 1989, pp. 1329-1335.
DISCLAIMERS
The citation of trade names and names of manufacturers in this paper is not to be construed as
official Government endorsement or approval of commercial products or services referenced herein.
39
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Intercomparison of remote and balloon-borne sensors operated at JAPE-91

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