6/21/06 #1

Basic Measurements

in

Progressive Science

Al Cooper

21 June 2006

6/21/06 #2

Measurements to Discuss

● Temperature

● Pressure

● Wind (Friesen)

– horizontal

– vertical

● Humidity

● Derived Variables

● GPS and D-values

– (Jensen)

● Dropsondes

6/21/06 #3

Temperature

● Five sensors available: TT_A, TTH{L,R}{1,2}

● TT_A comes from Gulfstream avionics (with

their processing)

● TTH are heated sensors, hence slow-

responding (>second)

● TTX is selected for use in derived quantities

like potential temperature. For PS, ==TT_A

6/21/06 #4

Processing Uncertainties

● Calibration! Based on bath calibration, but

there were inconsistencies still not

understood and problems with TTH

measurements

● Mach Number dependence: NOT used, but

expected. See variables TTH{L,R}{1,2}C

● Recovery factor: Used 1.0, but still fine-

tuning

6/21/06 #5

6/21/06 #6

6/21/06 #7

6/21/06 #8

6/21/06 #9

Suggestions, Temperature

(for now):● Use TT_A and associated variables. (Ambient T is

AT_A, and this is also ATX). No evidence of delay

or filtering in AT_A; seems as good as ATH for

response (unlike avionics pressure)

● Avoid ATHL1: many bad flights.

● Use caution for values <-60C for now. There is an

apparent calibration difference at T<-60., with AT_A

about 5C above others. There is also uncertainty in

the recovery factor, not yet resolved.

6/21/06 #10

Time response of heated sensors(here TTHR3)is obviouslyslow vs this

unheated (TTRL)one from TREX.

6/21/06 #11

Pressure:

● As for T, there is an avionics-supplied static

pressure: PS_A. The aircraft is “RVSM”

certified, which needs altitude accuracy of ca.

80 ft or, at 40Kft, pressure accuracy of ca.

0.8 mb.

● Pressure is measured independently as

PSFC (after corrections are applied). This is

the reference pressure used for Prog. Sci.

6/21/06 #12

6/21/06 #13

Other aspects of pressure:

● The avionics pressure PS_A is inherently

slow and has an evident lag, so it is best

avoided except as a reference for calibration.

● Beware of regular several-minute oscillations

created by the auto-throttles, which produce

oscillations in P, Z, TAS, and sometimes

other variables. (These are filtered from

PS_A.)

6/21/06 #14

Recommendation, Static P

● Avoid PS_A except for calibration: It has slow

time response and an inherent lag.

● Use PSFC (or PSX) for moderate accuracy.

● See the study to be presented by Jorgen

Jensen for higher accuracy, as needed for

combining pressure with GPS-altitude to

study pressure fields.

6/21/06 #15

Wind Measurements

● Dick Friesen will discuss in some detail

● Measurements look reasonable as first

estimates, but need (and are undergoing)

fine-tuning for such things as radome

calibration, removal of airspeed offset, and

an apparent but variable bias in vertical wind.

● Important qualification: Sensors are slower

than expected, don't provide >~5Hz

6/21/06 #16

Humidity

● Three measurements:

– DPLC and DPRC: dew point from chilled-mirror

instruments. 1/s samples used (serial); also

sampled at higher rate as analog output. “C”

refers to correction from measured frost point to

calculated dewpoint.

– TDL, provided in two channels with different

sensitivity. (archived as ppmv)

6/21/06 #17

DP sensors:* slow response * searching leads

to errors * reasonable match* lower DP than

prev.* P correction? * still, RMS<1.5C

6/21/06 #18

Beware of MR fluctuations:

● frost-pt values both

have floors at -74C,

which is d.p. of about -

87C

● As T changes, MR

changes, giving false

signal not representing

humidity changes.

6/21/06 #19

TDL:

● Does not have this lower-limit problem

● Calibration is independent of DPs

● Much more sensitive at low humidity

● Archived value is ppmv. Convert to MR in

g/kg by multiplying by 0.622E-3.

● vs DPs, values appear to be biased high?

6/21/06 #20

Comparison, MR from TDL and from DP

6/21/06 #21

Derived Variables: Some traps

● Be wary of MR fluctuations; they may not be

real for low values. Similar: q, RH, etc.

● Potential temperature is calculated from

AT_A and PSFC as in data files, and these

are best values. ATHxx and PS_A are less

suited to this calculation. Be aware of a

remaining calibration issue with T, though, at

low values: This still needs to be resolved.

6/21/06 #22

GPS position and altitude● Basic aircraft system provides high accuracy

● For best accuracy, differential GPS data are available,

but recorded separately and not yet part of the

processed files.

● There is high potential to use these measurements to

study pressure fields with good precision and spatial

resolution

● Errors are now such that the error in pressure is the

dominant source of uncertainty. See Jorgen Jensen's

talk for ongoing work on this source of error.

6/21/06 #23

Example● Geostrophic wind Wg=-(g/f) (dz/dn):

● measured D-value slope indicates about 80 m/s wind at

left, decreasing to right

6/21/06 #24

Dropsondes

● New installation encountered some problems

with sondes sticking in the exit tube and with

some striking the aircraft on release.

● System was modified, and after modification

mostly worked satisfactorily.

6/21/06 #25see ftp://ftp.eol.ucar.edu/pub/temp/users/kbeierle/progressive_sci/

6/21/06 #26

Expected Revisions:

● Wind: refinements underway (Friesen)

● Pressure: refinements underway (Jensen)

● Temperature: still need to resolve calibration, but

may not revise unless ATX=AT_A needs revision

● Higher-rate processing being implemented

● Differential GPS handling: may be merged to

primary dataset?