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%	4 %	2 ms
+Static Air Temperature	Rosemount model 102 non-deiced sensor (E102E4AL element)	+50 to –50 °C	0.006 °C	0.2 °C	2 Hz
Total Pressure (radome)	Rosemount  MADT2014MA1A	30 to 1300 mb	0.02 mb	0.25 mb	64 Hz
Total Pressure (aircraft)	Setra 270	0 to 1380 mb	0.07 mb	0.4 mb	10 ms
+Static Pressure	Rosemount  MADT 2014MA1A	30 to 1300 mb	0.01 mb	0.25 mb	64 Hz
+Dynamic Pressure: Radome – center/static port Aircraft - total/static port	Rosemount  MADT 2014MA1A Rosemount 12221F2AF	4 to 1000 mb 0 to 170 mb	0.02 mb 0.005 mb	0.50 mb 0.12 %	64 Hz 10 ms
Reference Pressure for Rosemount 858Y probes	Rosemount 1221F2AF	0 to 170 mb	0.005 mb	0.12 %	10 ms
Pressure Altitude	Rosemount 2014MA1A	-2000 to 75000 ft	0.5 ft	7 ft	32 Hz
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	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
+Pitch	(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
+ *Longitude	Litton 72 RH INS      (Binary Bus)	180 °	2.5 arc sec	0.4 nmile/hr	25 Hz

 

 

TABLE 2.   Derived Data Products

 

Parameter	Archived Resolution	Estimated Precision
+Horizontal Wind (u ,v)	10 Hz	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)	10 Hz	0.3 °C
+ *Virtual Potential Temperature (qv)	10 Hz	0.3 °K
+ *Pressure Altitude	10 Hz	20 ft
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	10 Hz   1 Hz   1 Hz   1 Hz	0.2 m/sec

 

 

 

 

 

Flush Radome Pressure System