C130 instrumentation report
This page summarizes instrument performance, which is detailled in the
RAF bulletin #9,
Standard Output Data Products . Also relevant are #3,
C130 overview & capabilities and #6,
Flight planning.
Instrument locations
x = B bottom, T = top
x = F fuselage
x = R radome (P for radome measurements is measured in nose, connected to the radome by semi-rigid tubing.)
x = W wing
x = X reference measurement used for derived calculations
xx = xD digital sensor
xx = xH a deiced (heated) sensor
xx = xL left, xR right
xx = RF reverse-flow (temperature sensor)
;
Aircraft variables
Here are the variables I use the most, with the instrument and accuracy.
Recommended sources are shown in green.
References to read are in brown.
-
Time UTC. Data tape reference variable.
-
Position
IRS Honeywell Laseref SM Inertial reference
system
-
Pitch, roll, heading accurate to .00034 degress. Ground speed to
.002 m/s
GPS Trimble Navigation Model
TANS IIIGlobal Positioning system (GLON, GLAT)
is accurate to 100 m, at a .5 m resolution (better for "steady state" conditions.)
-
Altitude
-
HGM232 radar altitude <
700m, spikes out above. Offset of around 6%. Accurate to .1
m.
Brown, E. N, M. A. Shapiro, P. J. Kennedy, and C.
A. Friehe. The application of airborne radar altimetry to the measurement
of height and slope of isobaric surfaces. Journalof Applied Meteorology
20, Sep. 1981, 1070-1075.
-
PALT
altitude above the geopotential surface derived from static pressure, using
standard atmosphere. A cleaner signal than ALT from the inertial
reference system or the scrambled GALT.
PALT = (Tref/gamma) [1.0 -(Ps/Pref)x]
Tref = 288.15K, Pref = 1013.246 mbar
gamma = standard lapse rate = 0.0065 K/M
Ps = measured static pressure, mbar
x = Ro gamma/(Mw g) = R gamma/g = 0.190284, g = gravity, M/s2
Ro = universal gas constant, R = gas constant for dry air 6.8557x10-2 cal g-1 K-1
Mw = molecular weight of dry air, g
CALT
Ian Brook's corrected pressure altitude fit to the radar altitude at low
level separately for each set of flight legs over the same ground track.
(6/12, 6/17)
Speed: From 5 radome differential-pressure gust-probes.
In data processing, GUSTO function uses the IRS and aircraft true airspeed,
angle of attack, and sideslip angle to derive wind components. Drift
due to IRS is corrected with GPS. Bias in pitch and sideslip removed.
Turns/climbs disrupt wind measurments. Resolution of turbulent comonents
of up to 10 Hz equivalent wavelength.
Brown, E.N., C.A. Friehe, and D.H. Lenschow (1983):
The use of pressure fluctuations on the nose of aircraft for
measuring air motion. J. Climate and Appl. Met.,
22, 171-180.
-
XUIC, XVIC east, north components.
Accuracy .1 m/s short term, 1 m/s long-term.
-
XWIC Better
for level runs WI
Better for sawtooths
-
XWSC Speed (not directly measured)
-
XWDC Direction wind is blowing from (not directly measured).
Discontinuities as the wind 'jumps' 360 degrees cause problems; recommend
using u and v components instead.
Temperature
ATRL (radome left)
Ambient air temperature from unheated Rosemont 102E2AL platinum resistance
sensor. Tries to decelerate the air adiabatically to zero velocity .
Not affected by interferance w/ plane's radio as is heated unit.
Well correlated w/ ATLL (+-0.2 oC difference in absolute temperature during
flight.)
Accurate to .5 C.
Calculated from the measured recovery temperature, which includes dynamic
heating effects, using conservation of energy for a perfect gas undergoing
an adiabatic deceleration process (adiabatic heating is about 5 C at 100
m/s). Neglect viscous heating outside of aircraft's BL. Can
be affected by wetting (2 C) and salt accumulation on the wire.
Flow distortion can affect flux measurments: Wyngaard,
J.C. (1988): The effects of probe-induced flow distortion on atmospheric
turbulence measurements:
Extension to scalars. J. Atmos. Sci., 45, 3400-3412.
Moisture
-
Humidity
-
Mean humidity
-
Thermoelectric dew point sensors
-
Fluctuating humidity
-
Lyman-alpha fast-response hygrometers. In-flight drift in the bias
voltage is removed by referencing it to more stable thermoelectric dew
point sensors. Do this for each profile, zeroing to the clean air
value.
-
Radome cross-flow unit: more reliable than stub. Use for mean.
-
MRLA
Mixing ratio
Derived. (grams of water vapor /kilogram of dry
air).
-
RHOLA Relative humidity.
Accurate to 5 %, resolution of 2%
-
Radome stub: faster response but more susceptible to in-cloud wetting and
thermal drift. Could use for fluxes.
-
MRLA1, RHOLA1 (6/12, 17 bad)
-
Dew point
DPBC (bottom fuselage)
Thermoelectric hygrometer, General Eastern Instruments 1011B. Fast
response, more limited dynamic range sensor. Less radio interference
& overshooting when humidity changed rapidly than DPTC.
Accurate to .5 C.
-
Liquid water content
-
PLWCC (left wing),
PLWCC1 (right wing) Corrected
cloud liquid water content from Particle Measurement Systems Model
KLWC-5 heated wire King probe. Varies with plane speed and
temperature. Each cloud penetration will require a baseline adjustment
with the relative change providing the sampled liquid water content.
Excludes ice. Derived by relating the power consumption (required
to maintain a constant temperature) to liquid water content, taking into
account the effect of convective heat losses.
Accuracy 0.02 g/m3.
Pressure
-
PSFDC (fuselage) Static pressure
calculated for local flow field distortion. Model 1501 (digital)
not affected by temperature sensitiviety. Original data accurate
to 1 mb, resolution of 0.034 mb.
Aerosols
-
FSSP Out of action for some of
the flights. Droplet concentration indicates cloud. In clear
air it should be less than 1 drop per cm3 (1Hz data) due to noise.
5 drops per cm3 can be classified as clear air (almost all maritime stratocumulus
will have N>5)
-
Radiation (more detail in RAF documentation, from which part of this section was taken)
RSTB1 is more
stable than RSTB. Thermal drift was stabilized by temperature-control
heater system.
Accuracy .5 C.
-
RSTB1C corrects the rstb1 for imperfect black
body radiativity, then adds .75
degrees, as in /worker/eight/coastal_waves/corr_rstb1.m. The
correction is verified by comparing bulk with direct fluxes, and by mixing
diagrams.
Radiometric SST from EG&G Heimann Optoelectronics Infrared Model KT19.85 bolometric radiometer. This must be corrected for 2 factors: the non-unity emittance and non-zero reflectance of sea surface, and the emission of IR
radiation by water vapor in the atmospheric layer between the
pyrometer and the surface.
Shortwave Radiation SWT, SWB is measured by modified versions of the
Eppley Model PSP pyranometers. Must correct for the effect of aircraft attitude on the measured down-welling. Aircraft maneuvers result in constant changes
to the attitude of the upward-looking pyranometer relative to the
position of the sun. At low solar altitudes, instrument can be blocked during manoeuvers.
Infared Radiation IRTC, IRBC
Measured by modified Eppley Model PSP pyranometers. Has been corrected to
remove the effects caused by the sink and dome temperatures.
Ultraviolet radiation UV Measured by Eppley model TUVR radiometers.
RAF bibliography
The data on this page is unpublished. If it is used please cite the
author Kathleen Edwards, the Center for Coastal Studies, and the Coastal
Waves group (David Rogers and Clive Dorman, PI's) at the Scripps Insitution
of Oceanography.
Please send comments or questions to me at kate@coast.ucsd.edu