NOAA WP3D AIRCRAFT - SLOW-RATE 1 HZ DATA (MATLAB)

C. Friehe (University of California at Irvine, USA)
S. Burns (University of California at Irvine, USA)
D. Khelif (University of California at Irvine, USA)

• Recalculated aircraft vertical velocity without using the baro-loop (s_vzi1c "& " s_vzi2c).
• Recalculated the vertical wind (using the recalculated vertical velocity) .
• Switched the dome and case temperatures for the Pyrgeometers - recalculated these temperatures.
• Dome and case temperatures for the Pyrgeometers used to calculate the incoming "& " outgoing longwave radiation.

Reprocessing on: 12 March 1996

• Introduced the revised empirical offsets for ambient temperature, and dewpoint temperature.
• Recalculated all thermodynamic variables and winds using these new offsets.

Reprocessing on: 8 March 1997

• Include prt5 voltage data and calibration coefficients.
• Include static pressure defect data.
• Recalibrated the Lyman-alpha to account for a 2 second time lag in the chilled-mirror dewpoint data.
• Recalibrated angle of attack -- to find a new vertical wind velocity (on N43RF).
• Recalculated all thermodynamic variables and winds using new offsets (slightly different than the values used in the March 12, 1996 version).

Reprocessing on: 8 July 1997

• Recalibrated angle of attack -- recalculated vertical wind velocity.

Data Access

From June 1996 on, data will also be available upon request from NOAA's National Climatic Data Center (NCDC)in Asheville, NC (http://www.ncdc.noaa.gov) and from the National Center for Atmospheric Research (NCAR) in Boulder, CO (http://www.ucar.edu/ucar/).

Background

Most of the missions were a mix of boundary layer and convective flight patterns depending upon the weather. Prior to mid-February, the majority of the convective patterns were at night, which precluded the collection of a large amount of boundary layer data. After mid-February, the convective missions were conducted during daylight hours so boundary layer and Doppler data were collected simultaneously.

The NOAA WP3D aircraft flight-level in-situ data, which are gathered by standard aircraft instrumentation, consist of measurements collected along the flight track of parameters such as air temperature, dewpoint temperature, position, altitude, etc., at a 1-sec data rate. The basic sensors and measured parameters include:

Parameter                       Instrument

Latitude, longitude             Two INS and one GPS system
Altitude above sea surface      APN 232 and APN 159 radar
altimeters
Aircraft attitude               static, dynamic, sideslip
and
				attack pressure sensors
Hor and vert accelerations      Two Inertial Navigation
Units
Air temperature                 Two Rosemount probes
Dew point temperature           Cooled mirror
Radiometer air temperature      CO2 radiometer
Sea surface temperature         Barnes PRT-5
Up/down radiation               Epply pyrohel
Electric field                  DRI field mills (up/down/
side)
Cloud water content             Johnson-William's hot wire

Data File Information

DATA_MATLAB/ - contains all processed data files in MATLAB
binary format
Documents/   - contains documentation about the data
Plots_var/   - contains PostScript time series plots of
selected variables
               described in paragraph above

DATE   CLASS    WP3D42 (H)     SIZE (MB)      WP3D43 (I)
SIZE (MB)

921102    1    921102Hs_P.mat     36.1       921102Is_P.mat
35.1
921106    3    921106Hs_P.mat     36.2       921106Is_P.mat
35.3
921113    0    921113Hs_P.mat     37.0       921113Is_P.mat
33.8
921115    0         none           -         921115Is_P.mat
36.3
921119    2    921119Hs_P.mat     32.0       921119Is_P.mat
26.6
921126    1    921126Hs_P.mat     34.6       921126Is_P.mat
36.4
921128    0    921128Hs_P.mat     32.5       921128Is_P.mat
30.3
921212    3    921212Hs_P.mat     37.1       921212Is_P.mat
35.6
921213    4         none           -         921213Is_P.mat
35.6
921214    4    921214Hs_P.mat     35.4       921214Is_P.mat
18.7
921215    4    921215Hs_P.mat     31.2       921215Is_P.mat
30.2
921216    1    921216Hs_P.mat     40.2       921216Is_P.mat
36.1
930109    1    930109Hs_P.mat     37.7       930109Is_P.mat
38.8
930111    1    930111Hs_P.mat     27.7            none            -
930116    1    930116Hs_P.mat     31.5       930116Is_P.mat
14.9
930117    1    930117Hs_P.mat     37.5       930117Is_P.mat
38.2
930118    1    930118Hs_P.mat     38.0       930118Is_P.mat
38.4
930201    0    930201Hs_P.mat     37.0       tape drive
failed     -
930206    2    930206Hs_P.mat     38.7       930206Is_P.mat
35.3
930209    3    930209Hs_P.mat     38.0       930209Is_P.mat
28.4
930210    3    930210Hs_P.mat     30.6       930210Is_P.mat
29.5
930217    2    930217Hs_P.mat     37.7           none             -
930219    1         none           -         930219Is_P.mat
37.0
930220    3    930220Hs_P.mat     37.2       930220Is_P.mat
34.2
930222    4    930222Hs_P.mat     30.3       930222Is_P.mat
31.4

For the slow-rate 1-Hz data, there are some 160 variables. A listing of these with definitions and units is available in the PostScript file Projects/Toga_Cepex/Documents/0togac_slow_var.ps and also in the ASCII Latex text file Projects/Toga_Cepex/Documents/0togac_slow_var.tex.

The variables are separated into four different types as indicated by the "a_", "c_", "s_" or "z_" prefix on the variable names:

- ASCII (string)                         ---->    "a_"
- calibration coefficients               ---->    "c_"
- slow variables (actual time series)    ---->    "s_"
- miscellaneous (housekeeping)           ---->    "z_"

a_aaf               s_mr_gef            s_tpygud
a_dpref             s_mruv              s_tpygudV
a_fldate            s_mruvcnts          s_trdprt5
a_ssaf              s_pdaf              s_trdprt5_orig
a_timeEND           s_pdar              s_trki1c
a_timeSTART         s_pdsf              s_trki2c
a_ttref             s_pdsr              s_tsrdco2
c_baaf              s_pitchi1           s_tsrdwin
c_bssaf             s_pitchi2           s_ttf1
c_kaaf              s_pqaf              s_ttf1_orig
c_kssaf             s_pqaf_orig         s_ttf2
c_laairf_ah         s_pqf1              s_ttf2_orig
c_laairf_dp         s_pqf1_orig         s_ttrV
c_ttth1             s_pqf2              s_ttth1
c_ttth2             s_pqf2_orig         s_ttth1V
s_aaf               s_pqr               s_ttth2
s_ah_gef            s_pqr_orig          s_ttth2V
s_ah_laairf         s_pqsf              s_tvir
s_azi1              s_pqsf_orig         s_vxg
s_azi2              s_pqw               s_vxg_orig
s_dai1              s_pqw_orig          s_vxi1
s_dai1c             s_psf               s_vxi1c
s_dai2              s_psfc              s_vxi2
s_dai2c             s_psw               s_vxi2c
s_dp_laairf         s_ptr               s_vyg
s_dpaocbf           s_pygd              s_vyg_orig
s_dpaocf            s_pygu              s_vyi1
s_dpegg             s_pyrdc             s_vyi1c
s_dpgef             s_pyrdr             s_vyi2
s_dpgef_orig        s_pyrdy             s_vyi2c
s_fstape            s_pyruc             s_vzg
s_hdgi1             s_pyrur             s_vzi1
s_hdgi1_orig        s_pyruy             s_vzi1_p3
s_hdgi2             s_rh_gef            s_vzi2
s_hdgi2_orig        s_rolli1            s_vzi2_p3
s_hg                s_rolli2            s_wdff1
s_hi1               s_sh_gef            s_wlgff1
s_hi1_p3            s_ssaf              s_wltff1
s_hi2               s_tad               s_wsff1
s_hi2_p3            s_tad_f1            s_wxff1
s_hpalt_psfc        s_tad_f2            s_wyff1
s_hr159s            s_tad_th1           s_wzff1
s_hr232             s_tad_th2           z_acnum
s_irsV              s_tasdf             z_class
s_jwlwc             s_tashf             z_fstindx
s_laairfV           s_tashfc            z_fstutc
s_latg              s_theta             z_min_size
s_latg_orig         s_thetae            z_offset_dpgef
s_lati1             s_thetav            z_offset_hdg
s_lati1c            s_timehp_run        z_offset_pqf1
s_lati2             s_timehp_ymdhms     z_offset_trdprt5
s_lati2c            s_timetc_01         z_offset_ttf1
s_longg             s_timetp            z_offset_ttf2
s_longg_orig        s_tl                z_pqnd
s_longi1            s_tpygdc            z_pqst
s_longi1c           s_tpygdcV           z_srate
s_longi2            s_tpygdd            z_utclacal
s_longi2c           s_tpygddV           z_utcth1cal
s_machd             s_tpyguc            z_utcth2cal
s_machh             s_tpygucV

0READ_ME		* A general description of the UCI processed
data.

0togac_slow_var.ps	* PostScript file of variables'
nomenclature used by
			  UCI.

0togac_slow_var.tex	* ASCII Latex text file of UCI variables'
nomenclature.

GPS_corr_uci.txt	* Sean Burns memo of Dec 20 1994 regarding
the UCI
			*  GPS correction of the INE groundspeed.

UCI_WP3D_memo.txt	* A copy of a memo similar to this one.

plot1.txt		* A Description of plot1_gpscomp_clr.ps and
			*  plot1_gpscomp_bw.ps

plot1_gpscomp_clr.ps	* A color PostScript plot comparing
the GPS correction
			*  scheme of UCI with that of NOAA/NSSL.

plot1_gpscomp_bw.ps     * A black and white PostScript plot
comparing the
			*  GPS correction scheme of UCI with that of NOAA/NSSL.

plot2.txt               * A description of
plot2a_windcomp_clr.ps and
			*  plot2b_windcomp_clr.ps

plot2a_windcomp_clr.ps  * Two color plots which compare the
calculated winds
plot2b_windcomp_clr.ps	*  by UCI, NOAA/AOC, and NOAA/NSSL
during a set of wind
			*  maneuvers.

plot3.txt               * A Description of
plot3a_windcomp_bw.ps and
			*  plot3b_windcomp_bw.ps

plot3a_windcomp_bw.ps   * Two black and white plots which
compare the
plot3b_windcomp_bw.ps	*  calculated winds by UCI, NOAA/AOC,
and NOAA/NSSL
			*  during a set of wind maneuvers.

921102	921126	921215	930117	930210
921106 	921128  921216  930118  930217
921113  921212	930109  930201  930219
921115  921213	930111  930206  930220
921119  921214  930116  930209  930222

TOGA COARE: 921113

         Aircraft 42 (H)
              1. 921113H_plt1 (3-D Flight Track)
              2. 921113H_plt2 (Navigation)
              3. 921113H_plt3 (Aircraft)
              4. 921113H_plt4 (Winds)
              5. 921113H_plt5 (Temperature)
              6. 921113H_plt6 (Humidity)
              7. 921113H_plt7 (Radiation)
              8. 921113H_plt8 (Miscellaneous)
              9. 921113H_plt9 (More Aircraft)

         Aircraft 43 (I)
              1. 921113I_plt1 (3-D Flight Track)
              2. 921113I_plt2 (Navigation)
              3. 921113I_plt3 (Aircraft)
              4. 921113I_plt4 (Winds)
              5. 921113I_plt5 (Temperature)
              6. 921113I_plt6 (Humidity)
              7. 921113I_plt7 (Radiation)
              8. 921113I_plt8 (Miscellaneous)
              9. 921113I_plt9 (More Aircraft)

Corrections

Trimble 2100 GPS systems were installed on the WP3Ds for TOGA COARE to allow for post-flight correction of the Inertial Navigation Equipment (INE) drift and Schuler oscillation. This was deemed necessary for the boundary-layer turbulence and mean wind data in TOGA COARE; it may also help the convection/radar flights. The GPS data were recorded at 1 Hz on the slow-rate data tape. Overall, they appeared to work well, although there are numerous spikes in turns probably due to the antenna angle changing in roll, periodic jumps with a 30-sec period, and a few unexplained periods of no changes.

UCI's initial processing technique was to correct only for the slow drift and Schuler oscillation (approximately 84-min period) of the Delco INE's with a zero-phase-shift low-pass filter using a cutoff frequency of 0.0005 Hz (33-min period) applied to the differences between INE and GPS positions and velocities. These filtered differences were then added to the original INE data to create "corrected" INE data. This procedure corrected a large percentage of the INE errors. Comments from the radar community (Dave Raymond) last fall stated that better corrections in turns were required. The use of an increased cutoff frequency was examined, and Sean Burns of UCI found by cross-spectral analysis that the GPS horizontal velocity data had a phase shift corresponding to a 1.2-sec time lag as well. (See memo from Sean Burns on 20 December 1994 about the details of the UCI correction scheme.) There was no phase shift between the GPS and INE position data. Accounting for the velocity time lag, which can only be done to the nearest second for the slow-rate data, showed increased improvement in the corrections. Additionally, increasing the low-pass filter cutoff frequency to 0.0025 Hz (6.7-min period) also was judged to further improve the correction without allowing significant errors due to spikes in the turns. In summary, the UCI GPS correction technique was to shift the GPS velocity data by 1 sec and apply the 0.0025-Hz zero-phase-shift low-pass filter to the position and velocity data. It is believed that this provides the best overall correction. Some of the egregious GPS errors which were found in a few flights were also manually corrected. The possibility of differentiating the corrected position INE data to obtain corrected ground speeds was examined, but it was found that excessive noise was introduced. The UCI GPS corrections were compared to those of NOAA/NSSL. The NSSL correction appears to retain the 30-sec periodic jumps and spikes from the GPS. A PostScript plot comparing the two GPS corrections to the east component of the groundspeed vector is available over ftp or the WWW.

The main effect of the GPS velocity correction is of course on the horizontal winds. The AOC-processed data have no GPS correction. NOAA/NSSL recently released a dataset which corrects the AOC winds with a variational GPS scheme. These data were compared to the UCI data. In many TOGA COARE boundary-layer flights, precise upwind/downwind maneuvers to check the winds were performed. These were used to obtain separate values for calibrations of side-slip angle sensors and dynamic pressure offsets for independent wind calculation. The comparisons indicate that the original AOC winds and those with the NSSL GPS correction do not pass the wind checks. Part of this may be attributed to dynamic and static pressure corrections used by AOC which is believed to be erroneous; the static pressure corrections obtained from the UCI-NCAR-AOC trailing cone test flights performed for the TOGA COARE project were used by UCI. In the convection flights, some upwind/downwind segments that were flown as a part of the research plan and the circle "pearls" were examined, and it was found that the UCI winds generally are acceptable at high altitudes and in other maneuvers as well. (There are exceptions when in heavy precipitation the radome and/or the fuselage sensors disagree perhaps due to water ingestion or icing.)

It should be noted that there are still unknowns in the WP3D winds. These arise primarily from the calibration of the side-slip angle and the heading accuracy from the INEs. The Delco Carousel IV INEs which have been used on the WP3Ds since they were built have a factory specification accuracy of only 0.4 deg in true heading. At 100 m/s true airspeed, this gives a wind error of 0.7 m/s. There is no independent heading reference on the WP3Ds. (Recall that a single-antenna GPS system such as the Trimble 2100 measures track angle, not heading.) Examination of the difference in heading between INE1 and INE2 reveals that they can drift during an 8-hour flight up to 0.35 deg apart. Also there is no record at AOC of the accuracy of the alignment of the heading of the INEs with respect to the aircraft axis, i.e., to the side-slip sensors. (Initially UCI thought there were errors in heading alignments, but chose instead to incorporate the equivalent biases in slip angles.)

Overall, upwind/downwind checks indicate that the UCI horizontal winds are good to about +/- 0.5 m/s in straight and level flight. Comparison of the UCI-WP3D winds with those from the WHOI IMET buoy, adjusted for the height difference, is also good. In the turns, accuracy is degraded due partly to some spikes from the GPS passing through the filter and unresolved errors as discussed above. PostScript plots comparing UCI, AOC, and NSSL winds for a set of wind maneuvers are available. It appears that the accuracy limit for the horizontal winds on a "production" basis for the 45 TOGA COARE WP3D flights has been reached. Some researchers may want to make detailed corrections for specific portions of certain flights on a case-by-case basis.

2. Air Temperature

The standard WP3D total air temperature sensors are the Rosemount de-iced hermetically sealed units. These have a slow response time, on the order of 1.6 sec. To obtain ambient temperature, a correction has to be made for dynamic heating which is about 6-12 K. This incorporates the dynamic pressure from a Pitot tube. The frequency response of the dynamic pressure transducers is 10 times greater than that of the temperature sensor (about 1 Hz for the co-pilot's fuselage Pitot), so that the calculated ambient temperature has high frequency "signal " that is erroneous (i.e., above about 0.1 Hz the total temperature signal is greatly attenuated and the dynamic heating correction is not applicable.) Therefore, for the purpose of the ambient temperature calculation only, the dynamic pressure was low-pass filtered (with zero phase shift) to match the response of the de-iced total temperature sensors. (There are two on each WP3D.) For the UCI-processed slow-rate 1 Hz data, these filtered ambient temperatures have been used for the calculations of all thermodynamic quantities.

For those wanting a faster-response ambient temperature signal, the UCI thermistors with response to at least 1 Hz are available in the UCI-processed data. (For a description of the thermistor sensor, see Fuehrer et al. 1994.) These were tailored to the boundary-layer conditions, so they sometimes go off-scale at colder, high altitudes. Also, they were subject to some radio interference. Please contact UCI if you are interested in using these data.

3. Humidity

Several humidity sensors were flown on each WP3D in TOGA COARE: UCI added a second-cooled mirror dewpoint (EG"&"G), a Lyman-alpha hygrometer (AIR); AOC added their own modified cooled mirror and installed the NCAR UV-hygrometer. For the slow-rate data, UCI used the AOC General Eastern "cooled mirror" signal in all calculations (humidity correction to true airspeed, thermodynamic variables, calibration of the AIR Lyman-alpha fast-response humidiometers.) The GEs exhibit the usual characteristics: slow response, oscillations, slow recovery from sharp transients, etc. For those interested in faster response humidity data, the calibrated Lyman-alpha signal (in terms of dew point and absolute humidity) is available in the 1-Hz dataset. Some cautions apply: at high altitudes one of them (on N42RF) oscillates. Also, the calibrations were obtained by a least-squares fit over a large portion of each flight where the dew point was > 0 deg C and there were no oscillations or other errors. Generally these are quite good, but some improvement may be possible for individual shorter segments and conditions where the dew point is less than 0 deg C. On some flights, especially later in the IOP, the NCAR UV-hygrometers appeared to work.

4. Radiation

In the UCI-processed dataset, the short and longwave radiometer data have been added, using the calibrations supplied by NOAA/AOC.

The short and longwave radiometer signals were not monitored during the TOGA COARE field experiment. In preparation for the subsequent CEPEX project in Hawaii immediately following COARE, CEPEX radiation scientists noted errors in the radiation signals and corrected these for N42RF, which was used in CEPEX. It is hoped that the CEPEX radiation scientists can provide a correction scheme for the TOGA COARE dataset.

Also, the UK C130 participated in TOGA COARE and performed some boundary-layer comparison flights on two days (17 and 18 January 1993). Dr. Phil Hignett of the UK Met Office has worked on some of the radiation data and finds that the downward longwave signal on N42RF had reverse polarity and a large offset. The shortwave radiation data agreed, although there is some question about the type of Epply colored filters on N42RF. It may be possible to use the excellent UK C130 radiometer data to obtain empirical corrections for N42RF, and then use the many close formation flights with N43RF to examine N43RF's radiation data. (The NCAR Electra comparison flights are another source.)

5. Empirical adjustments

Prior to the 1994 TOGA COARE International Data Workshop held in Toulouse, UCI made empirical adjustments to some of the aircraft measurements. The adjustments consisted of adding or subtracting a constant to/from the measurements. These offsets were determined from the many aircraft-to-aircraft intercomparisons in TOGA COARE with the goal of increasing the consistency between the various aircraft platforms. They are subject to further investigation and revision. The empirical offsets that have been used in the UCI data processing are summarized in the table below:

---------------------------------------------------------------------
UCI Empirical Adjustments for TOGA COARE
May 20, 1994

        Formula: X_adj= X_orig + Empirical Adjustment

Variable        N42RF           N43RF           308D
C-130
--------        -----           -----           ----            -----

 Total          ttf2            ttf1            N.A.
 N.A.
Temperature  (+0.35 C)       (reference)

 Ambient        N.A.            N.A.            atb
 None
Temperature                                  (-0.2 C)
(~ref)

 Dewpoint       dpgef           dpgef         dptc (ge)
 dp
Temperature  (-0.50 C)       (reference)        (~ref)
(~ref)

Sea Surface     prt5            prt5         rstb   sst_dh
sst
Temperature  (+0.80 C)       (+0.70 C)    (-0.70 C) (~ref)
N.A.
---------------------------------------------------------------------

Carl Friehe
University of California at Irvine
Department of Mechanical and Aerospace Engineering
Irvine, CA 92717-3975
USA

email: cfriehe@uci.edu
Phone: (714) 824-6159
FAX: (714) 824-2249

or

Sean Burns
University of California at Irvine
Department of Mechanical and Aerospace Engineering
Irvine, CA 92717-3975
USA

email: sean@cafws2.eng.uci.edu
Phone: (714) 824-7437
FAX: (714) 824-2249

or

Djamal Khelif
University of California at Irvine
Department of Mechanical and Aerospace Engineering
Irvine, CA 92717-3975
USA

email: dkhelif@uci.edu
Phone: (714) 824-7437
FAX: (714) 824-2249

Reference

 

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