ACE-1
NCAR C-130 - Project #6-130
Data Quality Report
by
Allen Schanot

This summary has been written to outline basic instrumentation problems affecting the data set and is not intended to point out every bit of questionable data. It is hoped that this information will facilitate use of the data as the research concentrates on specific flights and times.

The following report is organized into two sections. The first section lists recurring problems, general limitations, and systematic biases in the standard RAF measurements. The second section lists isolated problems occurring on a flight-by-flight basis.

Special pieces of User supplied equipment were used during the project and have been identified in the Research Instrumentation list included in this document. These data require special handling and it will be necessary to obtain access to the onboard operator notes for this information to be of use during the analysis phase. No attempt has been made to evaluate the performance of that equipment in this summary.

Section I: General Discussion

1. The wind data for this project were derived from measurements taken with the radome wind gust package. As is the case with all wind gust systems, the ambient wind calculations can be adversely affected by either sharp changes in the aircraft's flight attitude or excessive drift in the onboard inertial reference system (IRS). Turns, or more importantly, climbing turns are particularly disruptive to this type of measurement technique. Wind data reported for these conditions should be used with caution.

Special sets of in-flight calibration maneuvers were conducted on flights TF03 and RF14 to aid in the performance analysis of the wind gust measurements. The calibration data identified a systematic bias in the sideslip parameter. This offset, which resulted in roughly a 10 - 15 degree error in calculated wind direction, has been removed from the final data set. All of the remaining information, including the summary of IRS performance, indicated that the wind measurement system was performing within standard RAF specifications. The time intervals for each set of maneuvers have been documented in both the flight-by-flight data quality review and on the individual Research Flight Forms prepared for each flight.

As an additional enhancement to this data set, a second pass correction was applied to the wind data using position and ground speed updates provided by the GPS positioning system. Both the GPS corrected and uncorrected values are included in the final data set. RAF strongly recommends that the GPS corrected winds be used for all research efforts.

Two sets of vertical winds were also calculated (WI,XWIC). The two parameters are calculated using different aircraft vertical velocities. Under most circumstances the XWIC value will be significantly better. However, occasional spikes in the raw aircraft acceleration will produce atypical values. A quick comparison of the two variables will mark these occasions.

2. A Trimble Global Positioning System (GPS) was used as a more accurate position reference during the program. The system performed extremely well and the GPS position values should be used for all research efforts.

3. RAF flies redundant sensors to assure data quality. Performance characteristics differ from sensor to sensor with certain units being more susceptible to various thermal and dynamic effects than others. Good comparisons were typically obtained between the three standard temperatures (ATRL, ATRR, ATWH), two dynamic pressures (QCRC, QCFC), two liquid water sensors (PLWCC, PLWCC1), and the two dew pointers (DPT,DPB). Exceptions are noted in the flight-by-flight summary. The differences observed in the static pressures (PSFDC,PSFC) were typical for this type of project with the Model 1201 pressure transducer (PSFC) exhibiting its normal temperature sensitivity. The reference pressure used in all of the derived parameters (PSFDC) was obtained with a Model 1501 unit which was unaffected by these problems. The two remote surface temperature sensors (RSTB, RSTB1) were set up differently and there are periods when the two measurements differ significantly. The reference unit (RSTB) was heated during most of the project to reduce thermal instability at extreme ambient temperatures.

4. Temperature measurements were made using the standard heated (ATWH) and unheated (ATRR,ATRL) Rosemount temperature sensors All of these standard temperature sensors performed reasonably well, encountering the usual problems with sensor wetting during cloud passes. ATRR also experienced a certain amount of radio frequency interference (RFI) during broadcasts by the flight crew. ATRL and ATWH remained unaffected by this problem. A comparison of the data sets yielded good correlations in instrument signatures and only small differences in absolute value (+-0.2 oC) through out the program. A comparison of pre and post program calibrations indicated that all units maintained stable and independent calibrations. Due to its reliability and the lack of RFI interference, ATRL was selected as the reference value used in calculating the derived parameters.

5. Humidity measurements were made using two collocated thermoelectric dew point sensors and two Lyman-alpha fast response hygrometers. Generally speaking, the humidity sensors performed well when they were available. A series of hardware failures, however, prevented the use of the backup Lyman-alpha (VLA1, RHOLA1, MRLA1) for extended periods.

As is typically the case, the two dew point sensors (DPBC,DPTC) were set up differently to provide the best coverage under the widest range of ambient conditions. DPBC was set up for fast response, but its dynamic range was more limited. DPTC was a little slower but had the capability of measuring greater dew point depressions. DPTC, however, showed a tenancy to overshoot on rapid humidity changes. DPTC also experienced a certain amount of radio frequency interference (RFI) during broadcasts by the flight crew. DPBC remained mostly unaffected by this problem. A comparison of the data sets yielded good correlations in instrument signatures during the largest portions of the flights when both instruments were functioning normally.

Lyman-alpha hygrometers are susceptible to in-flight drift in the instrument's bias voltage. Due to this problem, RAF uses a special data processing technique to remove the bias drift by referencing the long term humidity values to one of the more stable thermoelectric dew point sensors. Occasionally an instrument will also experience a sudden baseline shift. These occurrences are rare, and are usually limited to the end of the life cycle of the units UV source tube. For programs focusing on clear air turbulence, the special processing technique can be set up to adjust for these "level shifts". For programs requiring routine cloud penetrations, however, the rapid changes in humidity or wetting of the sensor windows can trigger a reset of the coupling technique at an inopportune time. For the ACE-1 data processing, a broad limit was placed on the reference comparison which prevented proper adjustments for level shifts. Specific occurrences are identified in the flight-by-flight section of this report.

6. A set of upward and downward facing radiometers were used to measure shortwave, ultraviolet, and infrared irradiance. It should be noted that all units are hard mounted and that none of the data have been corrected for changes in the aircraft's flight attitude. Care should be used in identifying the aircraft attitude to determine a relative sun angle.

7. Thermal temperature chamber experiments have indicated that the Heiman sensors used to remotely measure the surface temperature (RSTB, RSTB1) are sensitive to some thermal drift. At cold housing temperatures ( T < 0 oC) some calibration drift is apparent. During prolonged intervals where the instrument housing becomes cold soaked, oscillations of up to +- 1 oC can also begin to show up. The mean value is typically OK, but the

fine scale structure can become lost in the noise. In an attempt to deal with these problems RSTB was equipped with a temperature control heater system. Generally speaking, the heater system stabilized the signal fairly well. At the warmer flight levels, both units show good agreement. When the signal diverge at the colder flight levels of the long range ferry legs, RSTB will provide the best measurement. Therefore, RSTB should be used as the reference surface temperature.

8. The altitude of the aircraft was measured in several ways. The primary measurement (PALT) is derived from the static pressure using the hydrostatic equation and the U.S. Standard Atmosphere. The inertial reference system outputs a similar measurement of altitude (ALT) by combining static pressure measurements with vertical acceleration. These outputs are well correlated and either may be used. RAF recommends PALT as the reference value, however, as it is typically a cleaner signal and uses the research grade static pressure sensor.

A radar altimeter (HGM, HGM232) was onboard the aircraft for the project, but failed to function. The unit was obtained from the military along with the aircraft and RAF was unable to bring it on-line by the ACE-1 deployment. None of the data have been included in the final data set.

The GPS positioning system also provides an altitude readout (GALT). The GALT signal has been "detuned" by the military and exhibits erratic oscillations of +-100 m. Due to these problems, RAF has decided not to include GALT in the final data set.

9. Two hot wire liquid water sensors were used on the C-130 during the ACE-1 program. The PMS King Probes (PLWCC, PLWCC1) worked extremely well during the program but experienced element damage on several flights with subsequent replacement. A comparison of the two units yielded an good correlation in instrument signatures and only small differences in absolute value through out the program. Special note should be made of the fact that both these instruments are calibrated for a specific range of aircraft speeds. Small changes in the baseline are apparent with speed changes, as are small zero offsets. Each cloud penetration will require a baseline adjustment with the relative change providing the sampled liquid water content.

Due to the nature of this sampling technique, it should be clear that water contained in ice particles will not be observed. This fact should be taken into account when comparing data from these sensors with the calculated liquid water content obtained from the optical particle probes.

10. The measurement of small CN size aerosol particle concentrations (CONCN) can be influenced by two effects. Droplet shattering during cloud penetrations can increase indicated CN concentrations by several orders of magnitude. Similarly, problems measuring the sample flow rate (FCN) will directly impact the concentration calculation. Difficulties were encountered with FCN during flights RF01 - RF15. However, the flow system used is functionally tied to the ambient pressure. Project data from the later flights were used to derive a replacement flow value (XFCN) to be used in the CONCN calculation during the flights in question. RAF has confidence that these data are relatively accurate. Clear air comparisons of the RAF system with Clarke's User supply systems (CN3010C, CN3025C, CN3760C) show excellent agreement.

11. Six PMS particle probes (FSSP100, FSSP300, 2D-C, 2D-P, PCASP, 260X) were used on the project. Some specific details on each of the probes are summarized below:

PCASP - Aerosol concentrations measured with the PCASP probe a(CONCP) are highly dependent upon the sample flow rate of the instrument. Recent modifications to the probe/ADS interface now allow RAF to monitor fluctuations in this flow rate directly (PFLW). Generally speaking, the size range of the CN counter is much broader than, but is inclusive of the sampling range of the PCASP probe. Therefore, intervals where CONCP exceed the value of the CN concentrations (CONCN) will be the result of some sort of sampling problem and are not a true measure of the aerosol concentration. The one exception to this restriction is in the marine boundary layer. Apparently the CN counter has a difficult time with the larger near surface marine particles. When the particle size distribution is dominated by the larger particles, CONCP can exceed CONCN by small amounts.

Note: While this probe was functioning throughout the project, the data are bad from flight RF01-RF16 due to leaks and other sampling problems.

FSSP100 - The FSSP cloud droplet probe functioned extremely well through out the entire project. Like all 1-D optical probes, however, the FSSP has no way to distinguish between ice and water. Therefore, the liquid water content calculated from this probe (PLWCF) should be used with caution in mixed phase clouds.

FSSP300 - The FSSP aerosol probe covers a range of particle sizes that bridges the gap between the true aerosols and the smaller droplets. The unit functioned extremely well through out the entire project. Like all 1-D optical probes, however, the FSSP300 has no way to distinguish between aerosols, ice or water.

Note: The bin sizes vary significantly in the particle sizing routines for this probe..

260X - The 260X precipitation probe has a tendency to be noisy in the first few bins. Generally speaking, concentrations from the 260X and 2D-C probes were well correlated. However, sporadic spiking did occur during many of the cloud passes. Care should therefore be used when interpreting these data. Like the FSSP probe, the 260X has no way to distinguish between ice and water. Therefore, the liquid water content calculated from this probe (PLWC6) should be used with caution in this application.

Note: The probe was non-functional during the Meridional Transect flights (RF01-RF10).

2D-C/2D-P - Both of the two dimensional imaging probes performed extremely well throughout the program. Due to the special nature of the 2D data set, only the digital computations of droplet concentrations have been included in the general data set. The actual image data have been archived separately. Access to the images will require the use of specialized software routines that may necessitate direct assistance from the RAF staff.

Darrel Baumgardner will be conducting a more detailed review of all of the RAF supplied particle measurement systems, including the MASP (designated as User supplied for this project). That review will be added to the archive at a later date.

12. The RAF was responsible for the ozone and carbon monoxide air chemistry measurements conducted on the C-130 during the program - (TEO3C;O3FSC;CO). Some atypical problems were encountered with these systems and they required some extra attention during the data processing an QA review. With the agreement of the ACE-1 Steering Committee, these measurements will be added to the data archive at a later date and a separate QA review will be conducted by the RAF Chemistry group.

13. Incidents of aircraft icing can be easily detected by examining the output of the Rosemount Icing Detector (RICE). Although may of the instruments on the aircraft are deiced, moderate icing of the instruments will significantly alter the performance characteristics of all of the available instruments. Moderate icing levels were encountered on several flights. Care should be used when examining data from these intervals.

14. Data recording typically begins well in advance of the actual aircraft takeoff time. Virtually all measurements made on the aircraft require some sort of airspeed correction or the systems are simply not active while the aircraft remains on the ground. None of the data collected while the aircraft is on the ground should be considered as valid.

** * * * * * * * * * *

Section II: Flight-by-Flight Summary

RF01 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

CAI shroud air speed iced up from 0050 - 0128 CUT.

Aircraft on ground for refueling from 2014 - 2105 CUT.

Data recording gap (4 sec) at 21:13:47 CUT.

RF02 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

CAI shroud air speed iced up from 1917 - 0214 CUT.

Drift in alternate surface temperature (RSTB1).

Level shift in Lyman-alpha (VLA, MRLA) @ 0125 CUT.

Tape recorder failure. Data gap from 240009 - 240414 CUT.

RF03 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

CAI shroud air speed iced up from 1832 - 2720 CUT.

Vertical Diff. Pressure (ADIFR) iced over. Wind data
bad from 1835 - 2156 CUT.

RSTB1 noisy with calibration drift.

RF04 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

RSTB1 noisy with calibration drift.

Alternate liquid water sensor failure (PLWCC1).

Data recording gap (16 sec) at 14:32:35 CUT.

Tape recorder failure. Data gap from 181855 - 183002 CUT.

RF05 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

Failure of alternate Lyman-alpha (VLA1, MRLA1).

RSTB1 noisy with calibration drift.

Oscillation in primary surface temperature (RSTB).

Top ultra-violet radiometer out for most of flight.

RF06 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

RSTB1 noisy with calibration drift.

QCR & ADIFR & INTAS1 iced up from 1900 - 1914 CUT.

Top ultra-violet radiometer intermittent during flight.

Excessive drift in IRS Longitude (LON).

Data recording gap (5 sec) at 18:30:12 CUT.

Data recording gap (2 sec) at 25:03:24 CUT.

Tape recorder failure. Data gap from 210628 - 211937 CUT.

RF07 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

RSTB1 noisy with calibration drift.

QCR iced up from 0234 - 0236 CUT.

Top ultra-violet radiometer out from 2250 - 2540 CUT.

Likely wetting of temperature sensors from 2406 - 2412 CUT.

Data recording gap (57 sec) at 19:02:45 CUT.

Data recording gap (18 sec) at 25:27:24 CUT.

Data recording gap (6 sec) at 27:01:19 CUT.

RF08 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

Wetting of sensor window in (VLA1, MRLA1).

INTAS1 & INTAS2 iced up from 2720 - 2845 CUT.

Top ultra-violet radiometer out from 2302 - 2704 CUT.

Data recording gap (4 sec) at 26:25:39 CUT.

Data recording gap (4 sec) at 28:11:01 CUT.

RF09 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

PMS FSSP100 probe was in-operative for whole flight.

Possible icing of bottom IR (IRBC) from 2445 - 2454 CUT.

Top ultra-violet radiometer out from 2522 - 2635 CUT.

CAI shroud air speed iced up from 2025 - 2521 CUT.

RF10 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

PMS FSSP100 probe was in-operative for whole flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

RSTB noisy.

QCR obstructed by water or ice from 2454 - 2507 CUT.

Data recording gap (27 sec) at 22:54:51 CUT.

Data recording gap (5 sec) at 25:05:49 CUT.

RF11 PMS 260X probe was in-operative for the whole flight.

PMS PCASP probe data bad for whole flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

RSTB & RSTB1 Noisy.

RF12 PMS PCASP probe data bad for whole flight.

PMS 260X probe experiencing excessive noise.

INTAS1 iced up from 0310 - 0330 CUT.

RSTB & RSTB1 Noisy.

RF13 PMS PCASP probe data bad for whole flight.

PMS 260X probe experiencing excessive noise.

QCR obstructed by water or ice from 0314 - 0326 and
. 0608 - 0626 CUT.

Possible water in sensor heads: DPB (0513-0520) &
DPT (0625-0628).

Level shift in Lyman-alpha (VLA, MRLA) @ 0258 CUT.

RSTB & RSTB1 Noisy.

Data recording gap (2 sec) at 01:12:02 CUT.

Data recording gap (17 sec) at 01:48:55 CUT.

Data recording gap (2 sec) at 03:03:43 CUT.

RF14 PMS PCASP probe data bad for whole flight.

PMS 260X probe experiencing excessive noise.

Possible water in sensor head DPT for flight.

Level shift in Lyman-alpha (VLA, MRLA) @ 0119 &
0145 CUT.

RSTB & RSTB1 Noisy.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

RF15 Possible water in sensor head DPT for flight.

Level shift in Lyman-alpha (VLA, MRLA) @ 0031 &
0131 & 0718 CUT.

RF16 PMS 260X probe experiencing excessive noise.

Level shift in Lyman-alpha (VLA, MRLA) @ 0030 CUT.

Bottom Ultra-violet radiometer out from 2236 - 3100 CUT.

RF17 PMS 260X probe experiencing excessive noise.

Possible water in sensor head DPT for flight.

Bottom Ultra-violet radiometer out for flight.

RSTB1 Noisy with calibration drift.

RF18 Possible water in sensor head DPT for flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

Some 10Hz noise in Lyman-alpha signal (VLA, MRLA).

Data recording gap (64 sec) at 15:30:58 CUT.

Data recording gap (7 sec) at 21:04:33 CUT.

RF19 Possible water in sensor head DPT for flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

PMS 260X probe experiencing excessive noise.

RF20 Possible water in sensor head DPT for flight.

Possible temperature sensor contamination from 1642 -
1737 CUT.

Level shift in Lyman-alpha (VLA, MRLA) @ 1648 CUT.

Data recording gap (8 sec) at 23:42:57 CUT.

RF21 Possible water in sensor head DPT from 2036 - 2340 CUT.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

Level shift in Lyman-alpha (VLA, MRLA) @ 1630 CUT.
RF22 Possible water in sensor head DPT for flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

Tape recorder failure. Data gap from 063353 - 063450 CUT.

RF23 Possible water in sensor head DPT for flight.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

Level shift in Lyman-alpha (VLA, MRLA) @ 1336 CUT.

RF24 Data recording gap (1 sec) at 20:34:36 CUT.

Data recording gap (5 sec) at 20:34:42 CUT.

RF25 INTAS1 obstructed by water or ice from 0608 - 0626 CUT.

RF26 INTAS1 obstructed by water or ice from 2053 - 2059 &
2756 - 2758 CUT.

Possible temperature sensor wetting (ATRR) from 2040 -
2053 CUT.

QCR obstructed by water or ice from 2629 - 2809 CUT.

Element damage to liquid water sensor (PLWCC). Baseline
offset with reduced response.

RF27 INTAS1 obstructed by water or ice from.2028 - 2300 &
2406 - 2547 CUT.

Bottom infrared sensor (IRB, IRBC) bad for flight.

Element damage to liquid water sensor (PLWCC). Baseline
offset with reduced response.

Data recording gap (8 sec) at 03:11:49 CUT.

Tape recorder failure. Data gap from 233057 - 233215 CUT.

RF28 INTAS1 & INTAS2 obstructed by water from.0147 - 0220 CUT.

Bottom infrared sensor (IRB, IRBC) bad for flight.

Element damage to liquid water sensor (PLWCC). Baseline
offset with reduced response.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

RF29 Bottom infrared sensor (IRB, IRBC) bad for flight.

Element damage to liquid water sensor (PLWCC). Baseline
offset with reduced response.

Level shift in Lyman-alpha (VLA, MRLA) @ 2204 CUT.

Excessive drift in alternate Lyman-alpha (VLA1, MRLA1).

RF30 Bottom infrared sensor (IRB, IRBC) bad for flight.

Element damage to liquid water sensor (PLWCC). Baseline
offset with reduced response.

DPBC beyond OPS range from 2206 - 2420 CUT.

Data recording gap (7 sec) at 22:07:16 CUT.

Alternate Lyman-alpha (VLA1, MRLA1) data bad for flight.

RF31 Bottom infrared sensor (IRB, IRBC) bad for flight.

Element damage to liquid water sensor (PLWCC). Baseline
offset with reduced response.

Alternate Lyman-alpha (VLA1, MRLA1) data bad for flight.

PMS PCASP probe data bad for whole flight.

Possible temperature sensor wetting or icing. Data
questionable from 2206 - 2348 CUT.

QCR & ADIFR obstructed by water or ice for intermittent
intervals from 2030 - 2425 CUT. All wind data
questionable through this interval.

INTAS2 obstructed by water or ice from.2150 - 2210 &
2237 - 2245 CUT.

Note: Aircraft crossed date line. Shift in LON from -180 to
+180 deg.

Tape recorder failure. Data gap from 225433 - 231256 CUT.

RF32 PMS 260X probe experiencing excessive noise.

PMS FSSP300 probe experiencing excessive noise.

PMS PCASP probe experiencing excessive noise.

Bottom infrared sensor (IRB, IRBC) bad for flight.

Element damage to liquid water sensor (PLWCC). Baseline
offset with reduced response.

Alternate Lyman-alpha (VLA1, MRLA1) data bad for flight.

Data recording gap (18 sec) at 21:01:02 CUT.

Data recording gap (6 sec) at 22:14:46 CUT.

RF33 Data recording starts in flight due to ADS system problems.

PMS 260X probe experiencing excessive noise.

PMS FSSP300 probe experiencing excessive noise.

PMS PCASP probe data bad for flight

Bottom infrared sensor (IRB, IRBC) bad for flight.

Element damage to liquid water sensor (PLWCC). Baseline
offset with reduced response.

Alternate Lyman-alpha (VLA1, MRLA1) data bad for flight.

QCR obstructed by water or ice from 1714 - 1805 CUT.