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The P-3B Turbulent Air Motion Measurement System
(TAMMS)
The TAMMS is composed
of several subsystems including: (1)
distributed pressure ports coupled with absolute and differential
pressure transducers and temperature sensors, (2) aircraft inertial
and satellite navigation systems, (3) a central data acquisition/processing
system, and (4) water vapor instruments and potentially other
trace gas or aerosol sensors. Table
1 contains a listing of the more significant parameters provided
directly by the TAMMS whereas Table 2 includes parameters which
are derived from the TAMMS data set. The attached block diagram indicates the placement
of selected TAMMS sensors aboard the P3-B and the paragraphs
below provide further descriptions of the individual system components.
Vector Air Flow - The angle of ambient air flow relative to the
aircraft is determined using the five-hole pressure port technique
as described by Brown et al (1983) and Larson et al. (1980). For this technique, five flush pressure ports (each with a diameter
of ~ 0.6 cm) have been integrated into the P-3B radome in a cruciform
pattern. Flow angle measurements, angle of attack and sideslip,
are obtained from differential pressure measurements made between
the pair of vertical aligned ports and horizontally aligned ports,
respectively. The center hole is linked to existing static pressure
ports on the side of the fuselage to provide required dynamic
and total pressure measurements. Hemispherical flow-direction sensors (Armistead and Webb, 1973;
Hagen and DeLeo, 1985) are mounted on the top and port side of
the fuselage just aft of the cockpit as a backup for the radome
airflow angle measurements. Static
and dynamic pressure measurements are also made with precision
sensors tapped into the aircraft total probe and static ports. All
transducers are installed in a structurally designed housing
open to the cabin environment and mounted on the forward cockpit
bulkhead. This minimizes the length of the pressure
tubes and allows the transducers to be maintained in a pressurized
and thermally stable environment.
Air temperature measurements
needed to determine true air speed, Ua , as well as heat flux
were made within a non-deiced total air temperature Tt sensor
housing using a fast-response platinum sensing element (E102E4AL)
with a nominal 50 ohm resistance (DeLeo and Werner, 1960; Stickney,
Shedlov, and Thompson, 1990). These
type of sensors exhibit a measured temperature Tm of (0.995Tt. Experimentally
obtained values of the recovery factor r for the temperature
probe indicates a value of 0.98 could be used over the speed
range of the airplane with minimal error (Barrick et al., 1996). A
second temperature sensor has
been installed to provide
redundant fast-response measurements in case the primary sensor fails.
Platform motion and position - A Litton Model LTN-72RH gyro-stabilized
inertial navigation system (INS) was retro-fitted to the P-3B
aircraft from the Electra aircraft for the present generation
TAMMS. The RH model has been primarily developed
for scientific applications with stringent requirements such
as those needed for accurate air motion measurements. It
provides an update rate of approximately 25 data frames/s on
both binary and binary-coded decimal (BCD) bus in ARINC 561 format. The position error drift is approximately
0.4 km/hr (personal communication from Charles Robinson of Litton
Industries, Inc.). It
is mounted inside the P-3B radome within an environmentally controlled
housing. The heading alignment of the INS has been certified to within 0.1(
by surveying the center line of the aircraft fuselage as transferred
to the ground surface.
Aircraft attitude angles
provided by the INS are electrically fed through a 16-bit synchro-to-digital
converter to yield angular resolution of 0.005 (for a platform
speed of 100 m/sec), an angular resolution of 0.06 ( is required
to provide 1 cm/sec precision
in vertical velocity). The
vertical velocity of the airplane wp is derived by integrating
the vertical acceleration output of the INS and bounding it by
the third-order barometric-inertial loop algorithm as suggested
by Lenschow (1986). The
long-term accuracy of the horizontal velocities up and vp are
dictated by INS drift rate. A
thorough discussion of inertial systems and the errors present
in the resultant velocity measurements are presented by Broxmeyer
(1964) and Kayton and Fried ( 1969). Lenschow (1972) gives a general discussion
on the types and orders of the magnitude of errors associated
with inertial systems.
In addition to the LTN-72RH
data, measurements of attitude, acceleration, and position
from the aircraft primary navigation system--a Honeywell laser-gyro,
inertial reference unit—are recorded as a backup. This
system does not have the accuracy or long-term stability of
the Litton unit, but does provide more rapid parameter updates
(50 Hz as opposed to 24 Hz) and real-time output of horizontal
winds that can be compared with TAMMS calculated winds for
periodic sanity checks. If
need be, data from this system can be used to determine three-dimensional
winds, however, preliminary calculations suggest resulting
vertical wind velocities are about a factor-of-two lower in
precision. The TAMMS also includes a global positioning system
(GPS) which provides Universal Time to +1 usec accuracy and
three-dimensional position to +100 m accuracy. These data are used as the primary time standard
as well as to correct the long-term drift in the INS position
measurements.
Data Acquisition System - Signals from the distributed sensors/instruments are routed to
a high-speed computer data acquisition system for filtering,
recording and processing. During
PEM Tropics A, the TAMMS the central processing system consisted
of a dual-processor SUN SPARC-20 workstation coupled to a VXI-bus
chassis containing analog-to-digital, ARINC 429, synchro-to-digital,
memory, and GPS modules. The SUN workstation communicated to the modules across a 6-foot
cable without shared memory capability which severely limited
acquisition speed and the potential for real-time processing
of data. We recently replaced the SUN with an imbedded 233 MHz Pentium III
PC that mounts within the VXI crate adjacent to the above mentioned
interface modules. The system is thus capable of communicating
directly to the interface modules across the VXI backplane
which, along with replacement of the previous non-buffering
analog-to-digital converter modules, has yielded about a factor
of 100 increase in data transfer rates. The resulting system is also designed specifically
for harsh environments.
During TRACE-P, we plan
to record a 50 Hz data set of filtered parameters which can
subsequently be averaged to produce 20, 10, and 1 Hz winds
and species measurements. In terms
of filtering, analog signals will either be routed through
an external 10 Hz Bessel filter or be greatly over-sampled (~6.6
KHz) then averaged to remove noise and unwanted high frequency
components. We are in the process of porting our post-flight
data reduction programs onto this system with the intent of
broadcasting calculated three-dimensional winds along with
running estimates of species flux across an ethernet connection
to other investigators aboard the aircraft.
Water Vapor Measurements - A Lyman-Alpha hygrometer (Buck,1976) manufactured by Atmospheric
Instrumentation Research, Inc (model AIR-LA-1AC) is used to
provide fast response water vapor measurements. A
slower response General Eastern 1011B hygrometer designed for
airborne applications is mounted in close proximity and used
to normalize the Lyman-Alpha signal.
System Calibration – Calibration/correction factors
and coefficients for the TAMMS system are determined from in-flight
maneuvers and measurements. As
noted above, the recovery factor for the air temperature sensor
was obtained by repeated passes by an instrumented tower a
varying airspeeds [Barrick et al., 1996]. The aircraft static
pressure measurement error was evaluated during a dedicated
calibration flight in which a long tube connected to a drogue
was trailed behind the aircraft to acquire comparative ambient
pressure measurements outside the influence of the airframe. For the radome and 858Y angles of attack and sideslip measurements, “k” factors
were determined by varying the aircraft pitch and yaw angles
in “porpoise” and “crabbing” maneuvers, respectively, at a
relatively constant altitude in quiescent air. Angle of attack “k” factors
were refined by performing very gradual speed variations at
constant altitude to systematically change the aircraft pitch
angle without perturbing its bow pressure wave at constant
altitude. Sideslip “k” factors
were fine-tuned by the constraint that calculated cross-track
winds be equal as the aircraft was flown in reverse headings
over the same ground track. Similarly, along-track winds from these reversed-heading
maneuvers were used to verify correction factors derived for
the aircraft static and dynamic pressure measurements. The
correction/calibration factors for the TAMMS are checked during
missions by examining calculated winds from turns and reversed
headings and by periodically performing porpoise and yaw maneuvers.
Displayed Parameters - In addition to display of
the parameters listed in Table 1, we intend to calculate and
provide three-dimensional winds in near real time aboard the
aircraft. Work is underway to incorporate the aircraft
true airspeed and vertical velocity correction algorithms into
the TAMMS data acquisition software so that winds of relatively
high accuracy can be calculated from the raw input signals. We
plan to provide wind information at 0.1 second intervals to
facilitate direct calculation of meteorological fluxes (see
below) as well as possible collection of air samples for analysis
and use in determining species flux via the eddy-accumulation
technique.
TABLE 1. TAMMS Sensor
Characteristics
|
Parameter
|
Sensor
|
Range
|
Resolution
|
Accuracy
|
Response
|
|
+Dew/frost point
|
GE 1011B Hygrometer
|
+30 to –50 °C
|
0.03 °C
|
0.6 °C
|
2 sec - 10 min
|
|
+Absolute Humidity
(Normalized w/GE1011B)
|
AIR-LA-1AC Lyman-Alpha Hygrometer
|
+50 to –60 °C
(dew point)
|
0.2%
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4 %
|
2 ms
|
|
+Static Air Temperature
|
Rosemount model 102 non-deiced
sensor
(E102E4AL element)
|
+50 to –50 °C
|
0.006 °C
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0.2 °C
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2 Hz
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|
Total Pressure (radome)
|
Rosemount MADT2014MA1A
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30 to 1300 mb
|
0.02 mb
|
0.25 mb
|
64 Hz
|
|
Total Pressure (aircraft)
|
Setra 270
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0 to 1380 mb
|
0.07 mb
|
0.4 mb
|
10 ms
|
|
+Static Pressure
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Rosemount MADT 2014MA1A
|
30 to 1300 mb
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0.01 mb
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0.25 mb
|
64 Hz
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|
+Dynamic Pressure:
Radome – center/static port
Aircraft - total/static port
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Rosemount MADT 2014MA1A
Rosemount 12221F2AF
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4 to 1000 mb
0 to 170 mb
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0.02 mb
0.005 mb
|
0.50 mb
0.12 %
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64 Hz
10 ms
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|
Reference Pressure for
Rosemount 858Y probes
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Rosemount 1221F2AF
|
0 to 170 mb
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0.005 mb
|
0.12 %
|
10 ms
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|
Pressure Altitude
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Rosemount 2014MA1A
|
-2000 to 75000 ft
|
0.5 ft
|
7 ft
|
32 Hz
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Pressure Altitude (Aux)
|
Rosemount 1241B
|
-1000 to 35000 ft
|
1 m
(at sea level)
|
0.4%
(0 to 4.5 km)
|
15 ms
|
|
Differential Pressure:
Angle of Attack (radome)
|
Rosemount 1221F2VL
|
50 mb
|
0.003 mb
|
0.1
|
10 ms
|
|
Sideslip (radome)
|
Rosemount 1221F2VL
|
50 mb
|
0.003 mb
|
0.1
|
10 ms
|
|
Angle of Attack (858Y)
|
Rosemount 1221F2VL
|
50 mb
|
0.003 mb
|
0.1
|
10 ms
|
|
Sideslip (858Y)
|
Rosemount 1221F2VL
|
50 mb
|
0.003 mb
|
0.1
|
10 ms
|
|
+ *Time
|
Bancomm bc637AT GPS
|
0 to 24 hr GMT
|
1 sec
|
2 sec
|
1 sec
|
| |
|
|
|
|
|
|
True Heading
Platform Heading
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Litton 72-RH INS : (Binary
Bus)
(Synchro)
(Synchro)
|
180 °
0 to
360 °
0 to
360 °
|
4.39E-2 °
0.1 °
0.1 °°
|
0.1
0.4
0.2
|
25
Hz
20
Hz
20
Hz
|
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+Pitch
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(Synchro)
|
180 °
|
0.04 °
|
0.2
|
20
Hz
|
|
+Roll
|
(Synchro)
|
180 °
|
0.04 °
|
0.2
|
20
Hz
|
|
Vertical Velocity
|
Litton 72-RH INS (Binary
Bus)
|
410
m-s-1
|
0.05
m-s-1
|
|
25
Hz
|
|
N/ S Velocity
|
Litton 72-RH INS (Binary
Bus)
|
1638
m-s-1
|
0.05
m-s-1
|
0.5
m-s-1
|
25
Hz
|
|
E/W Velocity
|
Litton 72 RH INS (Binary
Bus)
|
1638
m-s-1
|
0.05
m-s-1
|
0.5
m-s-1
|
25
Hz
|
|
+ *Latitude
|
Litton 72 RH INS (Binary
Bus)
|
90 °
|
2.5
arc sec
|
0.4
nmile/hr
|
25
Hz
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+ *Longitude
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Litton 72 RH INS (Binary
Bus)
|
180 °
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2.5
arc sec
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0.4
nmile/hr
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25
Hz
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TABLE 2. Derived Data
Products
|
Parameter
|
Archived Resolution
|
Estimated Precision
|
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+Horizontal Wind (u ,v)
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10 Hz
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0.2 m/sec
|
|
+ *Vertical Wind (w)
|
10 Hz, 1 Hz
|
0.2 m/sec
|
|
+ *Water Vapor (Q), g/kg
|
10 Hz, 1 Hz
|
5 %
|
|
+Static Air Temperature (Ts)
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10 Hz
|
0.3 °C
|
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+ *Virtual Potential Temperature
(qv)
|
10 Hz
|
0.3 °K
|
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+ *Pressure Altitude
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10 Hz
|
20 ft
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True Air Speed (TAS)
Variance(w)
Variance (water vapor)
Variance(Qv)
+ archived for TRACE P at 10
Hz
* archived for TRACE P at 1 Hz
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10 Hz
1 Hz
1 Hz
1 Hz
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0.2 m/sec
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Flush Radome Pressure System
![[Flush Radome Pressure System
]](images/image002.jpg)
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