The first and statistically most reliable step in the data analysis - the computation of the vertical phase lag between photospheric and chromospheric oscillations - was completed. Unfortunately, the error associated with this calculated phase lag is so great that the result has no physical significance. Since the subsequent data analysis that was originally planned would have much larger associated errors, it was concluded that the data available is insufficient to allow any meaningful results to be derived. Accordingly, the project was terminated. The reasons for the failure of the data are discussed. There are two basic reasons for this failure; (1) the very low signal to noise ratio of the raw data, and (1) the small statistical sample that resulted from the very small number of usable orbits. The final phase of data analysis is described. Finally, some comments and recommendations of a general nature are made concerning this entire contract effort. It is hoped that at least some lessons can be learned from this particular Guest Investigator project, so that future Guest Investigator programs can be pursued more effectively, and with less risk

Frazier, E. N.

English

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https://ntrs.nasa.gov/search.jsp?R=19780019216 2020-03-22T02:42:40+00:00Z
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(NASA-CR-157706) DATA ANALYSIS OF THE USP
	 N7E
XPERIKENI ON OSO-A Final Report (Aerospace
Corp., Los Angeles, Calif.)
	
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I'HL AEROSPACL (A)RPORRATION
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Aerospace Report No.
ATR-78(9461)-4
Data Analysis
of the
LPSP Experiment on OSO-8
FINAL REPORT
Prepared by
E. N. Frezier
1 JUNE 1978
Space Sciences Laboratory
The Min A. Getting Laboratories
THE AEROSPACE CORPORATION
Los Angeles, California 90009
This work was supported by the National Aeronautics and
Space Administration under Contract No. NASW-3067
hL
10, -1k—. a .
".	 ugge. Ilea,'
1 trop7hysics Depart ent
XA
. P4ulikas, Director
Space Sciences Laboratory
Aerospace Report No.
ATR-7819461)-4
Data Analysis of the LPSP Experiment on OSO-8
Prepared:
E. N. Frazier
.Astrophysics Department
Approved:
r
Table of Contents
Page No.
1. Summary
	 1
.	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .
The 0SO-8, Labor-!toire de Physique Stellaire et Planetaire (LPSP)
Data from Orbits 1330, 1331, and 1315 , , , , , , , , , , , , , , , , 1
3. The OSO-8/SPO Phase Lags . . . . . . . . . . . . . . . . . . .
	
3
4. The Source of the Meaningless Results , , , , , , , , , , , , , , , , 5
5. General Recommendations	 .6
Figure Captions .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 . 9
Figures	
.	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	 .	
10
k
1. SUMMARY
The first and statistically most reliable step in the data analysis - the computa-
pion of the veritical phase lag between photospheric and chromospheric oscillations - has
been completed. Unfortunately, the error associated with this calculated phase lag is so
great that V,e result has no physical significance. Since the subsequent data analysis
that was originally planned would have much larger associated errors. it was concluded
that the data available is insufficient to allow any meaningful results to be derived.
Accordingly, the project has been terminated. The reasons for the failure of the data
are discussed. There are two basic reasons for this failure; 1) the very low signal to
noise ratio of the raw data, and 2) the small statistical sample that resulted from the
very small number of usable orbits.
The final phase of data analysis ;s described. Finally, some comments and
recommendations of a general nature are made concerning this entire contract effort. It
is hoped that at least some lessons can be learned from this particular Guest Investigator
project, so that- future Guest Investigator programs can be pursued more effectively, and
with less risk.
2. THE OSO-8, LABORATOIRE DE PHYSIQUE S'TELLAIR ET PLANETAIRE (LPSP)
DA'iA FROM ORBITS 1330, 1331 AND 1345
Orbits 1330, 1331 and 1345 were the only three orbits from this program where
usable data was obtained from the same area on the Sun simultaneously by OSO-8 and
Sacramento Peak Observatory (SPO). :accordingly, data analysis concentrated on these
three orbits. The hope was that if this analysis was successful, the results would indicate
-1-
some technique by which conclusions could be drawn from the remaining data despite the
fact that the two instruments did not view the same region of the solar surface. This
hope was not to be realized.
Data from each of the three primes orbits was extracted from the 'apes and
reformatted into a time sequence. Due to the low count rate of the LPSP instrument,
the time sequences were integrated over the internal raster scan of the LPSP telescope,
thereby sacrificing all spatial information on the oscillations in an effort to gain
maximum signal-to-noise in the subsequent temporal analysis. Samples of these time
sequences from each of these three orbtts are shown in Figure 1. Each of the orbits was
programmed slightly differently in accordance with the original intention to acquire a
variet y of data.
Orbit 1330 emphasized time variations in the orofilc of the Mg 11 k line. To
increase sensitivity, the wide exit slit was used with the result that the other channels
were sacrificed. (In this configuration, the other lines are shifted away from their
respective exit slits, and only continuum is observed.) In Figure la, the difference
between the counts in the blue wing and the counts in the red wing, which is proportional
to line of sight velocity, is plotted. The long term drift caused by the orbital motion of
the satellite is obvious. Oscillations with a period of three to five minutes are not
obvious.
Orbit 1331 emphasized the Lya profile. as before, the other charnels wcee
sacrificed in order to scan the I_y a profile with the wide exit slit. The blue :wing-red
wing difference is shown in Figure lb. Despite the integration over x and v and the use
of the wide exit slit, the count rate wi.s still so low that the result was almost pure
noise.
-2-
Orbit 1345 was devoted to , search for rapid oscillations. Therefore the grating
was held fixed and the exit slits arranged so that the core of the 119 it h line came
through a wide exit slit. This data is shown in Figure le. The count rate is indeec ` ► igh.
but rapid oscillations are not obvious.
The power spectra of all the time sequences from the three prime orbits were
calculated to search for the presence of oscillatory power. Sample power Spectra are
shown in Figure 2. The means and linear trends have been ;ubtracted from the data prior
to Fourier transformation. Figure 2o, the Lya and velocity power spectrum is a
textbook example of white noise combined with large statistical fluctuations. The
Mg II k, velocity and Mg II h intensity power spectra display some oscillatory power in
the frequency range of 4 to 10 mHz, in addition to residual low frequency noise. Of all
the power spectra. that of the tilg II k velocity data from orbit 1330 (Figure 23) appeared
to display the statistically most significant oscillatory power. Therefore, it was selected
for comparison with the ground based dgta.
3.	 THE OS0-8;'SPO PHASE LAGS
The very first step in the comparison of the OSO-8 data with the SPO data is to
calculate the phase lag and therefore the time delay between an oscillation observed in
the photosphere (SPO data) and that same oscillation observed in the chromosphere
(OSO-8 data). Such an observed phase lag leads directly to an observed phase velocity in
this crucial altitude range. The technique for calculating this phase lag was to cross
correlate the two data sets as H function of time lag. This cross-correlation is shown in
Figure 3. Specific:illy, this particular pair is orbit 1330. velocity in the photospheric line
-3-
FeX 3468 cross-correlated with velocity in Mg II k. Both time sequences were observed
simultaneously at the same 10 x 10 ar.: sec patch on the sun. It is important to note that
of all the possible pairs of data chat could be cross-correlated, this particular pair was
carefully selected in order to provide the best possible cross-correlation. There appears
to be it reasonable cross-correlation for time lags betweer, -500 sec and *500 sec which
indicates that the chromospheric velocity oscillation lags the photospheric oscillation by
about 140 ;ecofW .
1t this point, the critical question is: [low accurate is this observed phase lag?
To calculate this accuracv, the standard technique of Goodman (1957) * was emploved.
This technique require: the intermediate calculations of coherence and phase spectra of
two fluctuating quantities and furnishes a statistical basis for estimating 80 116 "confi-
dence limits" (essentially 'lo error bars) of the phase lag at any chosen frequency. These
confidence limits are a function of the degree of coherence and the number of
statistically independent samples available. For the cross-correlation of Figure 3, the
coherence in the frequency range where power exists at all is only 60%. which is very
low for such a cross-correlation analysis. The number of statistically independent
samples is, of course, one. From this. the 20 error bars on the 14 second time lao can
be calculated: 1'10 seconds! This means that the phase lag could be anywhere from
essentially zero to 370 seconds. StaEed physically, the waves in the solar atmosphere
could be either standing waves or traveling waves with virtually any physically possible
phase velocity! No physical conclusion can be drawn from this phase la; analysis.
Goodman (1957) Scientific Papers No. 10, Engineering Statistics Laboratory, New
York University.
-4-
Since this phase lag was ?alculated from the best pair of time sequences, any
further phase lag calculation would be even less meaningful. Likewise, the next
expected step in the analysis, the calculation of oscillatory energy flux at different
heights in the atmosphere, requires a knowledge of vertical phase velocity at several
heights, and would be subject to even greater error than this single, "best", phase lag.
The only other result expected from this project, the change in horizontal scale of the
oscillations with height, was sacrificed at the start of the analysis when the data was
integrated over N• and y in order to improve the signal to noise ratio.
We are finally driven to the conclusion that the basic data set is not adequate to
(.erive the simplest conclusion about the height dependence of the oscillations. The
project has been terminated.
4.	 THE SOURCE OF THE %IE KINGLESS RESULTS
Why did the data fail so completely to reveal anything lbout the chromospheric
oscillations' There are two fundamental reasons. The most obvious reason is the high
noise level that resulted from the low sensitivit y of the LPSP instrument. This noise
level completely obliterated the Lya signal (Figures lb and 'lb) and seriously degraded
the VIg lI data. It is also probable that this noise level is responsible for dc,cr(:asing the
coherence between the Mg II k time sequence, thereby incr"asing the error in the phase
lag to an intolerable level.
The second basic, though less obvious, reason is the to sampling sta• .sties that
resulted from the fact that only three orbits worth of usable data were collected.
Furthermore, each of these three or its had been pro(,:°am,ned to coll^ct data in a
T
-5-
different line, so the results from the three orbits could not be averaged together. How
serious was the effect of this low sample' The best idea van be obtained by considering
ground based observations of photospheric oscillations, which by now have a very long
and well de(!umentcd history. In nearly all original data records, it can be seen that
oscillations are present with significant amplitude about one third of the time. With only
three orbits worth of data, this project had, at best, an even chance of seeing any
oscillations at all! On top of these odds, the lack of any capab i lity to average over more
than one observed set of wavo trains probably doomed the analysis effort.
.5.	 GENERAL RECOMMENDATIONS
Despite the fae'- that nothing was learned scientifically from this project, there
are still some ir.:portant !essons to be learned about how to conduct a Guest Investigator
project. To put this question in perspective, it should be remembered that OSO-8
sponsored the most ambitious Guest Investigator program ever attempted by NASA, and
that this particular Guest Investigator project involved some of the most sophisticated
operational and data analysis techniques ever attempted with any satellite. Therefore. it
must be expectod that this project pioneered considerable :.>w r, and in the utilization
of sat-llites by Guest investigators. It is therefore important to ask how successful the
overall operation was, and what difficulties were encountered that should be avoided in
the future.
In retrospect, it is clear that this project was too sophisticated for a Guest
Investigator effort. It entailed .00 many requirements for near-nominal operation of the
atol'it^ instrument. In othc, words, the project v.as not desi gned to "degrade
o acefully". F inec n guest Investigator has no respoonsibility or authorit; over the
-j-
design and operation of a satellite instrument, it would L,e n mistake for him to design in
observing program that requires nominal instrument performance. The "pioneering"
experiments should clearly be left to the principal investig • itor and his tea:n.
One other major recommendation emerges from the experience Rained in this
contract. There should be much greater communication an(. cooperation between Guest
Investigator and Principal Investigator before, during and alter the execution of the
Guest Investigator's observing program. The idea that a Guest Investigator can come to
a sr tellite control center, operate the instrument for a f-^w days, then take his data
home for analysis, is naive in the extreme. In this particular project alone, there were
many Specific instances (which xill be left undorumer.ted) where the attempt to operate
in this "individualistic mode" resvo.od in inefficiect operation of the satellite, degraded
data and duplication of effort. The prime example of this inefficiency is probably in the
early phase of the data analysis. A significant portion of the funds in this contract  was
expended writing computer programs to read the satellite data tapes, refcrmat and
calibrate the data, etc. These prograr-.s probably were a ,i exact duplication of thost,
written by the P.I. team. .1 combined programming effort would have been far more
cost effecti.e.
From the stand point of efficiency and quality of data, there appears to be no limit
to the desiraUility of closer P.I.-G.I. cooperation. It seems more effnctivc therefore to
^,rganize a rather formal team consisting of the P.l. and all the G.Ls fairly early in the
life of a satellite program, with the overall tasks and we individual responsibilities
spelled out clearly. Tt.e G.I.s should be allowed co become closer members of the
"team", and the P.I. should be able to expect greater assistance from the G.Ls as well as
significant involvAment in the scientific results. Furthermore, as future satellite
instruments beconno even more complicated and scphisticated, it can be expected that
this requirement for more coordination and organization will become even more severe.
-8-
In conclusion, it coin ue paid ti,"t this entire project pushed a little too iuird in
several different directions, and as a result all that was learned Were 30MC ICSS011S about
how not to push too hard in the future.
,.)
i
Figure captions
Figure 1. Samples of raw Data from each of the three prime orbits. (a) Orbit
:330, velocity measured in the wings of the Mg 1I k line. The units are the difference
between the counts in the blue wing and in the rea wing. (b) Orbit 1331, velocity
measured in the wings of the Lya line. The unit.: are the Same 3s in (a). (c) Orbit 1335,
intensity of the Mg 1I h line. Intensity is measured in counts.
Figure 2. Power spectra of the data displa}-ed in Figure 1. The mean and linegr
trends were removed from the data before the power spectra were calculated. Power is
expressed in arbitrary units. On l y orbit 1330. (panel a) displays significant oscillatory
power.	 ,per power represents either noise or long term drifts.
Figure 3. The cross-eorrelation between 'he OSO-8 data (orbit 1330, NIg II k
velocity) and the Sacramento Peak Ohservator y data (Fe?. 8368, velocity) taken
simultaneously from the carne patch on the sun (10 .irc sec x 10 arc sec).
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Data analysis of the LPSP experiment on OSO-8

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