Determination of
Martian Surface Reflectivity
From 0.4 to 1.1 Micron
Using a Vidicon Spectrometer
by
Douglas John Mink
Submitted in
Partial Fulfillment
of the Requirements for the
Degree of Master of Science
at the
Massachusetts Institute of Technology
May, 1974
/
U
'
Z
-.
vr
n Planetary Sciences, May 20, 1974
Department of Ejrth
Cer t i f ied by: -w
W-9
Accepted by:
Chairman, Departmental Commi ttee on Graduate Students
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pag .
Determination of Martian Surface Reflectivity from 0.4 to 1.1 Micron
Using a Vidicon Spectrometer
by
Douglas John Mink
Submitted to the Department of Earth and Planetary Science
in part-ia.I fulfillment of the requirements for the degree of
Master of Science on May 23, 1974
ABSTRACT
A new astronomical instrument, the vidicon spectrometer,. is
being developed at the M.I.T. Planetary Astronomy Laboratory.
Based on the silicon diode vidicon system currently in use there,
a low dispersion prism is added between the vidicon image tube and
the telescope, allowing digital vidicon photographs to he taken df
spectra.
These spectra are stored on magnetic tape and computer
processed to create intensity vs. wavelength curves for stars -Ind
The high spatial resolution of the vidicon imagle tubte,
planets.
combined with a higher spectral resolution than photometer fil ters
currently -inuse at M.I.T. give this instrument potent ial in the
study of planetary surface composition from spectral ref lectivitt..
Procedures for reducing the vidicon images to spectra have bf'en
tested on a set of spectra of tio stars and the planet Mlars.
It
is concluded that the viclicon response is not linear enough wi th
variations In exposure time at lot, levels of incoming light for
consistent star spectra. although it works well with Mars clue to
the planet's larger intensity where the vidicon tube has i ts
The spectrometer slit is so narrow (one seconr
poorest response.
of arc for this data) that uaveleng.th-dependent
var iations in
refraction of light from a point source by the atmosphere .caw1r'e
,tar spectra of variable clualitl.
Because of the lou quality of
the star spectra. direct spectral rrflectivity measurenwnts (which
are obtained using Mars to star ratios) proved to be impossible.
Although further tests of the spectral and intensi ty response of
the silicon dinde Vidicon should be carried out in the laboratory
before good results can be gua-anteed, the presont Mars spectra
may probably be used in conjunction With photometer-derived
reflectivity data to expand coverage of the surface of Mars.
Thesis Advisor: 'Thomas B. McCord
Title:
Associate Professdr of Planetary.Physics
page 3
Acknowledgements
Numerous people were involved in the design and construction
of the.vidicon spectrometer, although I have only met a few.
Professor Thomas B. McCord, Mr.
Jeffrey Bosel,
and Ms.
Carle
Pieters have been informative about the design of the hardware,
as
well as the conditions under which they obtained the Mauna Kea
data.
Dr.
Robert Huguenin lent his insight into the problems of
Martian surface composition, as well as criticizing an early draft
of this thesis.
spectrometer,
Stevp Kent, who i4 also working with the
provided criticism and astronomical knowledge.
My
spouse. Catherine, has greatly aided me financially' and morally.
while David McOonald greatly expedited the production of this
thesi.s. with the aid of several computers.
pag' 4
Table of Contents
I. Introduction
page 5
II. The Vidicon Spectrometer-
page 9
111.
page 16
Image Processing
IV. Anal-ysis of Data
V.
Recommendat ions for Future Use
page 27
page 50
page 5
1. Introduction
surfsce
about
infrared
the
as
experiments
such
From
composition.
of
quantity
learned
was
little
Mars,~
planet
the
information about
vast
a
returned
has
9
Mariner
Although
spectrometer., particle size and silica composition were estimated,
but these. determinations had error bars
useless
so great as to be
nearly
composition
of the
conclusions about
In reaching
surface materialso-f rars.
the
Until the Viking Lander in 1976, there
is no way to physically look at a Martian rock with instruments.
moot
Probably the
technique
useful
for
surface composition is reflectance spectroscopy.
that
limonite,
constituent.
a
hydratdd
Dollfus (1961),
reflected by Mars ,
studying the polarization of light
oxide,
iron
was
sensing
remotely
concluded
a major
probably
Hovis (1365) observed absorption bands in the near-
infrared reflectivity of limonite and suggested that they would be
a
diagnostic
test for
limonite
on Mars.
Sagan
et
al
(1365)
compared absorption pands they observed in laboratory specimens of
lisonite to Dollfus'
surface
data.
microns
Martian albedo curves
a
with at least some limonite was not inconsistent with the
Adams (1968) observed absorption bands between 0.5 and 2.5
in
many iron-bearing
varied significantly from
caused
and concluded that
by electron
minerals,
mineral to
transitions in
the positions
mineral.
iron ions
bands i.n hydroxyl iokns and water molecules.
of which
These bands
are
and by vibrational
Adams suggests
that
page G
the
absorption feature observed in Tull's (1966) geometric albedo
curve is not inconsistent with a hydrated basalt composi tion.
The
feature observed at one micron in their spectra is not due to iron
Adams anrd
in iron oxides, but to iron ions in silicates.
(1969),
opposition
They
that
concluded
obtained
during
the
for
bright
aras
the
the dark areas
those from
of the
was
the surface
and hydrated
0i;7
ihad
Mar ti:in
conposed
of a
oxides.
The
iron
composed of of the
were modelled as being
and dark areas
same.material
curves
oxidized basalt
combination of
bright
that
discovered
different shapes than
surface.
albedoes
geometric
using
McCnrd
in different degrees of oxidation.
McCord and
see
(1971,
Westphal
and
Elias,
McCord,
also
Westphal, 1971) observed Mars during the 1969 opposition and noted
that the iron ion absQrp-tions were in different places,
compositional
and three
differences.
bright,
each
indicating
Seven areas were observed,
five
being about
Martian
four dark
longitudinal
From this data, much compositional analysis
degrees in diameter.
has been. done (see Figure I for examples of mineral ref lectivities
compared
to
Mars);
generalizations about
Despite
over
of the
the rest
Hellas basin remain uncovered;
coverage
at
higk
$pectral
sample,
small
obtained during
made.
be
the 1973
as the Coprates canyon
what
and
is needed is tihole disk
A
new
has been developed to obtain
the
and
technique, vidicon spectroscopy,
a
surface cannot
spots
twenty additional
opposition, such interesting features
the
such
from
however,
spatial
resolution,
page 7
-j
MOAB
.
ARABIA
I
-
tI li-
0-
..
-
5
U-
1.00
0
z
4w
--
0.00
0
z
S10J
'003
0.3 0.5
11
WAVELENGTH (p)
-j
.4.
0.5
.O
WAVELENGTH (p)
AREA 59/74
Cr.
iiIfifif
-
01wI )J
N3
*-*0
~
1.00-
0.00
1
L
t
-1
0.3 05
WAVELENGTH (p)
Figure 1.
Comparison of Mars
dark area reflectivity
to reflectivity of sheet
silicates. Note resemblance to the clay minerals, kaolinite and montmorillonite.
(Courtesy Dr.Robert
Huguenin)
1.5
'
)
WAVELENGTH (Mm)
page 8
desired high resolution ful -disk coverage.
that technique.
This thesis describes
page 3
11. The Vidicon Spectrometer
The
silicon diode array vidicon *was originally developed for
television and picturephone use, but because of its large
range,
high quantum efficiency, and
used by a growing number
linear response, it is being
of astronomers as a digital
for photographic plates.
factor
as
and
McCord
development
of
a
at
photography
and
on
an
RCA
Planetary
(see
silicon
Figure
developed as a
sets
similar
reflectivity
for
2).
tube
those
work at
reported
Using filters
used
MIT.
Kunin
on
the
Laboratory
with
of
the
This system
a
peak
with
this
system
photometer,
photometers
As reported
would give the
by McCord
1.1
has been
using
for
is
quantum
sloping off to about 6% at
two-dimensional imaging
to
(1972),
single-frame astronomical
Astronomy
vidicon
vidicon spectrometer which
the
have
a
the resolution-
Technology (MITPAL).
efficiency of 85% at 6.5 microns,
microns
(1973)
vidicon system
the
are
McCord and Westphal
Bosel
Massachusetts Institute of
based
however, that is not
atmospheric conditions
limiting factor in astronomy.
(1972),
replacement
The only advantage a photographic plate
has over a vidicon is spatial resolution;
limiting
dynamic
filter
spectral
and Bosel,
spatial resolution
a
of
vidicon combined' with a greater spectral resolution than such
a vidicon photometer is under development.
The vidicon spectrometer
is attached
telescope.
to
the
front
is basically an optical syctem
end of
Schematically it consists
the
vidicon
system
of a low-dispersion
which
on the
prifm
page 10
>4.
20
0.~~4.4
+
.
+
6008
.012
WAVELENGTH IN MICRONS
Figu re 2.
Quantum
efficiency of the RCA vidicon.
This is the percentage of incoming photons which
the diode array and affect it as opposed to being
reflected or passing through without being absorbed.
This graph was made by averaging the published
curve over 250 angstrom segments.
. page 11
through 'hich 'light from
a slit
telescope is passed.
dispersed image
refocused
onto
The
the
surface
practice this is done
situatecIat
of
the
of the
the focus
of the
vidi con
slit is
then
diode array.
In
through a system of mirrors (see Figure
3
for detai ls) to avoid the infrared absorpt ion of lenses.
The
vidicon tube consists of a 1024 by 1024 array of revereae
biased diodes.
A photon impinging on the vidicon target
in a decrease in charge i n the diode
read out by scanning the diode
recharges
the
diodes
array wi th an ele ctron beam
as it hits
them
prod ucing
known.
which
current
a
By knowing where
the
inten si ty at eac h location in the
is at any given time, the
diode array 'can be
The image is
it reache s.
proportional to the amount of charge Ios t.
beam
resul'ts
These
intensity elements
are
then
passed on to be recorded and displayed (for further detai Is on the
electronics
of a silicon vidicon
see Crowell and Labuda (1363)).
The vidicon is read out as 250 rows of 256 image elements,
which corresponds
physically to
four diodes.
resolution
less accurate
positioning
scan,
electron beam.
still
In
each of
such a
is required
loier
of the
No data is lost, and the vidicon's resolution
better than the atmosphere allows.
is
The intensity image is
amplified, recorded on magnetic tape, and displayed on a slow scan
TV monitor.
processing.
A
This image
for further
computer
The spectrometer system is diagrammed in Figure 4.
portion of
Figure 5.
is then available
a vidicon
The elements
spectrometer image
along the column
is presented in
correspond to
spatial
page 12
CAMERA
image is
in focus
BAFFLES
LOW
DISPERSION
PRISM
SPHERICAL
MIRROR
BAFFLES
VIDICON '
image is
in focus
here
Figure 3. Optics of the MITPAL vidicon spectrometer.
The telescope is to the right.
Figure 4.
The MITPAL vidicon system with the spectrometer attached.
page 14
elements along the slit.
Wavelength is along the abscissa.
The
magnitude of each element is proportional to the current from
vidicon
the
diode array at the time a corresponding diode uas read by
the scanning electron beam.
into a spectrum.
The image is now ready to be
turnerd
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111.
Image Processing
that must be
first processing
The
convert the " column
is
This
wavelength.
coordinate into
image is
done to the
to
clono
through the use of a calibration function:
S= -SO+
So,
,
and
=) +
0
(X'- xO)
(S+ So)-
C being. three constants determined
from three column
number-wavelength correspondences as fol lows:
C =N(
-
) (St+ SO) (S2+SO)
so-St+(XXS
($-
- $St)
(4-t4)(S2-Si)( -
S
Si-X)
6 -
A)
So.= -S + (C -9 $ - 2
C
9
..
These correspondences are obtained
show4n in Figure
periodically
G).
From
is known - (see Figure
7 .for
as a function of
varies
Figure 8 for a sample
sharp emission lines fav
this calibration,
as data is taken,
spectrometer
by observing the
lamp with known
of a calibration
image
0
S -i
which
is
redons:
the wavelength-column relationship
an example).
wavelength, as
The
resolution
would be
also
expected (see
dispersion function plotted from the
first
derivative of the calibration function).
Now
enough is known to process a spectral
image.
A program
0.
64.00
Figure 6.
98.00
128.0
VIDICON COLUMN
180.00
192.00
2N,
A spectrum of the calibration source, indicating vidicon intensity
of each vidicon element along one row. Assigned wavelengths are
indicated.
I.0
V1DCu)2
F.125
Sir 35.0 La
LC=
0.1541
0.3139
?
1 0.3145
;. 31,f
4
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1
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203
201
153
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51 - C.3508
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52
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0.4357
Figure
7.
0.5190
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185
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246
247
248
229
22~1R
250
Wavelength as a function of vidicon column
for a typical calibration function. The three
column(Sn)-wavelergth(Ln) tpairs used to
determine the function are given at the top.
Columxi number is at the left, wavelength at
right,
2.5758
2.1256
2.8937
3.0862
3.1077
page 19
300
280
260
240
220
z
200
0
o 180
z
0
U
160
W 140
Z 120
,
100
80
60
40
20
0
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
WAVELENGTH IN MICRONS
Figure 8.
Spectrometer dispersion function.
spectral. resolution per image element
as a function of wavelength.
1.1
1.2
page 20
Planetary
subroutine under the
runs as a
has been written which
Laboratory's image processing system (DIPSYS) which has
Astronomy
images
been set up to provide a metastructure under which vidicon
may
be easily
appears in Figure 9.
by
DIPSYS
A simplified diagram
processed.
of this program
The spectral image is read off the run tape
on a disk
and stored
spectral processing routine,
to the
where it is available
three basic
which has
The
tasks.
first and easiest is to punch out the intensities along one row of
the
into a plotting routine
cards for input
image onto computer
Second,
(this was how Figure 6 was produced).
column by
the image,
average background from
it
can subtract the
column, where
the
rows over which the background is to be averaged are read from the
input
instruction cards.
the program
most important,
Last, and
can produce a new 'image in which all of the elements have the same
spectral resolution.
range
interest is
of
angstroms,
the
best
0.4 to
1.2 microns,'
resolution
at
a resolution
microns,
1.2
of 250
chosen.
was
10 and 11 show the effects of this processing on an image
Figures
of the standard star Xi 2 Ceti.
integrated spatially
telescope
along
optical effects,
Portions of these images are then
the slit.
Due
a star image
to
is not
a point;
is at its maximum where the point source would be.
the full energy output of the star at a given wavlength,
must be integrated across
all rows where
and
atmospheric
smeared out spatialy into to a Gaussian distribution of
which
the
reflectivity work, where
For spectral
it is
intensity
To use
the image
the image intensity
is
Figure 9.
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Ceti
0. 35S to 0 . 7 0p.
Each image element represents intensity perfrom
ten angstroms averaged
over a 230 angstrom resolution element. The background was
first
subtracted out of the vidicon image.
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page 24
above the background.
After this integration, the spectrum vector
is punched out onto cards for plotting and further processing.
more advanced
version
of
this processor
will
incorporate
A
the:'
plotting, ratioing, and other functions into one OIPSYS subsyste~m.
where only disk files will be used.
The
final
procedure needed
spectral ref lectivi ty
is to know from what part of
data of the surface of a planet
surface
for good
the
A photograph is taken through
the spectrum originates.
the eyepiece, loeking at the slit in a mirror tilted 45 clegrees to
the optical axis of the telescope (the first surface in Figure 3).
A similar
plotting
logging arrangement
program has been written to
coordinate grid of
disk
is used
A
create Calcomp plots of the
Mars (or any other planet)
projected onto
a
using the physical ephemeris of the planet from The American
Ephemeris and Nautical Almanac
Universal
Figure 12
Time.
while Figure
13
output.
position the
To
projected
is a typical,
onto the 'grid,
point the -original
resolution
and the
spectra
time of
is a block diagram
although
observation
on the
than
normal,
ditk of .the
photograph of the telescope image
and the slit
vidicon images have
of stars
and
is
marked by hand.
At this
been reduced to
constant
known positions
reduction to spectral reflectivity data,
in
of the program,
smaller
spectrometer slit
planet, the negative of the
begin.
data.
for photometer
on Mars;
as well as testing,
and
can.
page 25
PHYSICAL
EPHEMERIS
(1 MONTH)
CREATE TABLE OF
SUB-EARTH POINT
COG~RDINATES AND
APPARENT DIAMETER
ADD HOURLY CHANGE
OF PARAMETERS TO
TABLE
RUN CAR D:
day of month
UT start of run
UT end of run
Lcaption
Figure 12.
Flowchart of grid
plotting program.
CA LCULATE POSITION
LOF SUB-EARTH POINT
CALCULATE NUMBER
OF MAPS TO BE DONE
(one per five minutes)
DRAW LINES OF LATITUDE
in spherical coordinates,hold
$ constant and rotate in 6.
transform so that sub-earth
point is at 0=900, 6=00 and
project to plane.
DRAW LINES OF LONGITUDE
in spherical coordinates, hold
6 constant and rotate in $.
transform as with latitude lines.
WRITE CAPTION
object, time, sub-earth point,
apparent diameter in arc-seconds.
LOG MAP and INCREMENT TIME
GET NEW RUN CARD and
CHECK FOR LAST INPUT
MRHS
VIDSP EC C
4 OF 4
0 CT. 18, 1973
T= 8: 58 UT
LRT= -17.3
LONG= 9. 8
DIA= 21.46 SEC
Figure 13.
A typical grid plot produced by the program in Figure 12,)
the third produced for vidicon spectrometer Mars run C.
page 27
IV. Analysis of Data
The
to use the
first major attempt
vidicon spectrometer to
take spectra for reflectivity work occurred during the
On two consecutive nights the Mauna
of Mars during October, 1973.
Kea
trained on
reflector was
eighty-inch
opposition
Mars, and
the planet
about 75 spectra were taken, as well as an equal number of spectra
Alpha Lyra and Xi
of the standard stars
2 Ceti.
Xi 2 Ceti
was
chosen because it was near Mars in the sky, while Alpha Lyra has a
Figure 14 demonstrates the reduction
ratios to get reflectivity.
get spectral
used to
methods
raw intensity
reflectivities from
To avoid airmass reductions, spectra of Alpha Lyra
spectra.
Xi
is used to calculate planet/sun
which is well known and
spectrum
and
2 Ceti were taken when the two stars were at -the same airma!-s,
1.38.
little variation with
Since star/star ratios exhibit
airmass
changes, the ratio
spectra can
also be
airmasses.
Before
extensive
usable.
testing
used
any data
was
stars obtained from these
of the two
to
reflectivities
reduce
was
done to
see
loai
reduced
to
whether the
-it oth-r
reflectivitin-.,
data
would be
This portion of the thesis will describe that work,
usinV;
the best results obtained to date.
Figure 15
shows a high resolution
spectrum of
Alpha
Lyrat
which has been averaged over 258 angstrom segments to simulate the
spectrometer output.
vidicon
spectrometer
Figure 16 is an Alpha Lyra spectrum from the
from which
the
vidicon response
has been
page 28
AIR MASS CORRECTED SPECTRA
Figure 14. Production of spectral reflectivity from
raw spectra. Air mass correction not
not needed if objects to be ratioed are at
the same air mass.
page 29
+
+
wlfs
+
+
:
>
.0;
+0
+
+
8+
+++
+
+
+
WAVELENGTH IN MICRONS
Figure 15. Spectrum of aLyra, averaged over
250 angstrom resolution elements, from
a 50 angstrom resolution spectrum provided
by Steve Kent.
page 30
in
.W)
(1>
Crn
Q. ZO
0.40
WR,-VELFNG1
0. b
TI
IN MrI6h.C
Figure 16. aLyra spectrum from vidicon spectrometer
with vidicon response (Figure 2) divided out.
page 31
broader to about 0.7
shape is generally
and that the
wavelength
longer
slightly
to a
is shifted
the peak
Note that
removed.
To test the repeatability of the data, pairs of spectra
microns.
Results of one such
of the same star were ratioed to each other.
to
pair are shown in Figure 17 (all ratios plotted are normalized
Figure 17a is the ratio of two Alpha Lyra
1.0 at 0.S75 microns).
but different exposure
spectra with similar airmasses (1.40/1.38),
If
times (Ssec/lsec).
linear,
be. flat.
would
It is obvious
relatively flat region
the
integration
of the
spectra, so
(exposure) time,
peak intensities
a 'pedestal'
idea,
was
set up
under
nonlinear features of the
and 17c show the results of
respectively
Figures 17b
pedestal doesn't help at
registerable
to 0.8
from 0.5
all.
and
again the
energy,
different
exposure
curve is relatively
a
is 403S).
microns,
but
a
Figure 18 shows a similar
ratio for two Xi 2 Ceti spectra with slightly different
(1.67/1.32)
400.
installing pedestals of 300 and
to help
All
possibly,
and
curve would go away.
maximum intensity
300 seems
p)edestal of
lIarger
(the
To test
the spectrum..
intensities below a certain value would be ignored,
the
of
signals are nonlinear
that low level
representations of the intensity received from the star.
this
curve
the
however, .the
that it is not;
corresponds with the
it may be
perfectly
given source is a
if intensity recorded from a
that is,
linear function
the response of the system were
airmaq'es
times (20sec/15reec).
flat over
the peak
this time from almost 0.4 to 0.8 microns.
in
Once
incoming
(Figure 19 is a
page 32
4.
+
++++++++44.4
4.4.4.
4.
4.
4.
4.
C,,
U.'
z
4.
++
.20
0.40
O'.EENG0 .60
0O.80N
WAVELENGTH IN MICRONS
SRLTR86
U
1.00
/ SRLYR83
Figure 17a. Ratio of two aLyra spectra, all elements
above background included.
U
1.20
page 33
CD
.g.~.g. 4~.g*
+
4.4.
4.
+
4.
4.
I
U,
zLU
+
~6.
'rn-Go
81
bko
Sf1
-0o.40
00so
08o.
WAVELENGTH IN MICRONS
SRLTR86
/ SRLTR83
Figure 17b. Ratio of same two aLyra spectra,
this time including no elements less than 300.
1.20
page 34
4.
~4*
4.
co
0
RI-.
zc
C-~
B'
"b2
- ----
EEG
I
M6icR
WAVELENGTH IN MICRI
SALYR86
- - - - ----
1.00
'
SRLTR83
Figure 17c. Ratio of same two a Lyra spectra,
this time including no elements less than 490.
1.20
page 35
4~
4+
4.
b-n
zwi
44444444+4.
PI
Cie
81
U44-
,b'.a0
0WAVE
'.GT
N C'.S
WRVELENGTH IN MICRONS
SXCT112
SXCT124
Figure 18. Ratio of two t2 Ceti spectra, including
all image elements above background.
.4.
page 3G
typical
2 Ceti
Xi
smooth upturn
spectrum).
which has
that there is some idea as to
Figure 20
be observed.
rather than
be, the Mars
two stars'
is
spectra.
while
This is because the stars are both of spectral type AO,
sun,
summed
Note that the peak
like the
the blue
spectra
Mars spectrum,
is a typical
over five vidicon elements down the slit.
in the red,
the reliability range of
though it may
the spectrometer, indefinite
Thut .
from 0.4 to 0.8 microns.
g0
can
significance.
some undetermined
star ratios seem to be usable, at best,
Now
is a
however, there
this time,
the
which is providing the light which is ref lected from Mars is
21 shows a saturated spectrum
a cooler, redder type G. Figure
peak intensity of
'The
Mars.
although around 1.1
microns,
it was thought
Originally
could
saturated spectrum
unsaturated
microns.
spectrum
which
The data show,
overlap
that
be
from 0.5 to 1.0
4095 is surpassed
microns,
had
the signal is
to extend
a very
signal
unluckily, that there
of a
of
range
the
low
unsaturated.
portions
the unsaturated
used
of
an
beyond 1.1
is little or
no
between the good signal from one and the good signal from
the other type of spectrum.
Once again, an attempt was made to do
away
signals
with
22a.b,and
low,
nonlinear
c show the progressive changes
400 are subtracted
images
seem
to be
from the original
more consistent
Figures 23a,band c and
different
with
'images of Mars
a
pedestal.
as pedestals of 300 and
spectrum.
than
24a,band c are
to each other.
Figures
Ratios of
those of
star images.
the results of
The
Mars
ratioing
three images used
page 37
4.
+44.
+
+
x
+
+
+
g .20
0,40
0.60
0.80
*
WAVELENGTH IN MICRONS
SXCT112
Figure 19.
INTEG.
A typical t2 Ceti spectrum. Note that
the peak is at a longer wavelength and
the shape is broader than a Lyra.
.00
L..
page 38
0.
'U).
U)i
I-
z
9ll
"b.
,jL ,
,
,
+++++
++
o.co
0o.o
WAVELENGTH IN MICRONS
SMRISC-4
INTEG.
Figure 20. A typical Mars spectrum
I
LOU0
'
1.20
page 39
(39
.b20
9-4.
0.40
+
+
0.60
0.80
1.00
WAVELENGTH IN MICRONS
SMARSC-5 I NTEG.
Figure 21. An overexposed spectrum of Mars.
Arrows indicate intensities reading greater
than 4095 in at least one element of the image
which went into the resolution element.
1.20
page 40
aim
+
4am
4am
o1
a
.
0.
z
t-8
aim,
'b'2o
WRAVELENGTH IN MICRONS
SMRRSC-1 INTEG.
Figure 22a. Mars spectrum
L.20
page 41
4.
ag-i.
4.
+
00.
W0
x W4
+
4.
4.
Si
9.20
AA
A
A
I Iv1
A
0.40
4
0.0
-I
0.80
ARVELENGTH IN MICRONS
1.00
SMRISC-1 INTEG.
Figure 22b. Mars spectrum with pedestal of 300.
1.20
page 42
+
.4.
a'.
0
C)
3-
+
+
U)
El.
+
SI
EU
.20
~U
EU
0.40
U
(U.60
j
0.80
.0
AAVELENGT4 IN MTC9ONS
SMRRSC- i INTEG.
Figure 22c. The same Mars spectrum with a pedestal
of 400.
.2
page 43
were taken within 15 minutes of each other.
the
image was used in each case.
Note the
flat curve
repeatability
than
from 6.5
for the
above a nonlinear level.
the
apparen.tly good data
recoverablei.
micron,
stars, possibly
indicating
due to
better
more signal
pedestal is increased, some
is lost, but
time a pedestal of 400 is used (c).
of
Each is a one minute exposure.
to 1.1
As the
The same portion
the noise is
of
gone by tho
The Mars spectra are probably
page 44
++++++++
++++ ++++
++++
+
I-
-
i
.20
0.40V'e
0ONS
WAVELENGTH IN MICRONS
1.00
SMRRSC-4 / SMRSC--1
Figure 23a. Ratio of two Mars spectra.
1:20
page 45
++++++++++++
+++
-1
Cra
z5
W&
20
R.20
0V40ELEGT
WAVELENGTH
SMRRSC-4
Figure 23
41
0N8MICR
IN MICRONS
SMRRSC-1
Ratio of two Mars spectra, each of which
has a pedestal of 300.
b.
1.20
page 46
++++B4+++++++++++
+44
I-Cs
C,
zv
ch2o
& a
& a
.:d
& a
A
o'.
'.o
WAVELENGTH IN MICRONS
i'.od
SMRRSC-4 / SMRRSC-1
Figure 23c. Ratio of same two Mars spectra, this
time with a pedestal of 400 under each.
a
A
a
a
'
'
'
''.
a
page 47
+
"'4'+
+
+++++++++
+
+4'
Cf)
ze5-
8I
b.2o
muI
0'.0
0.80
0.80
WAVELENGTH IN MICRONS
1.00
SMR9SC-9 / SMARSC-1
Figure 24a.
Ratio of two Mars spectra, without pedestals.
1.20
page 48
++++++++++
-~
I
wc;
si
"t.20
''O'.
o'o
o'.o
WRVELENGTH IN MICRONS
p
I
to0
SMARSC-9 / SMRRSC-1
Figure 241). Ratio of two Mars spectra, each of which
has a pedestal of 300.
p
p
p
1.20
page 49
+++
++.+
-
00
-
81
0.
0.o W
*
6
a a a a
-
-
--
WAVLEGTso I
a A N 2 a a
'.O
I'0
WRVELENGTH IN MICRONS
SMRRSC-9
SMRESC-1
Figure 24c. Ratio of same two Mars spectra, each of
which now has a pedestal of 400.
1.20
page 50
V.
Recommendations
for
Future
Use
of
the
Vidicon
Spectrometer
Although it appears that it will be impossible to do spectral
work
reflectivity
inability
the
using
vidicon
spectrometer
stars and planets
to meaningfully ratio
to
due
an
over a useful
range, the instrument has advantages which will make it worthwhile
The combination of good spectral resolution
to develop it.
angstroms
or
photometer), with
resolution
to 300
compared
better,
complete
angstroms
spectral coverage
indicate much promise.
It
and
(250
for
a filter
high
spatial
appears tha.t the limiting
factor will be the response function of the vidicon tube, with its
nonlinearities in wavelength and intensity.
Once more lab work is
done to quantify knowledge about this problem, the instrument will
be ready to gather more
data.
Another problem which may
affect
the star spectra is the problem of differential diffraction of the
star's
light.by the
earth's atmosphere.
Different wavelengths,
diffracted at slightly different angles would show -up at different
positions in the
smeared out star
spectrum, and if
the slit
is
smaller than the apparent diameter of the star, part of the stat '
spectrum would be lost, in a wavelength-preferential manner.
solution is to widen
at
the slit;
the vidicon would be reduced,
although the spectral
The
resolution
the spectrum would he much mi e
reliable. But what about the Mars data from Mauna Kea?
With the
high spatial resolution and apparent good response of the vicdirdon,
something should be recoverable.
The planet in the slit occupi e-
page 51
up to 35
seconds
elements in a
vidicon column
in diameter, and the slit
good seeing of 1.5 seconds or less,
spectrometer image.
when it
is
about 23
is two elements wide,
arc
so, wi th
there are fifteen spectra
per
Luckily, the slit passes over some photometer
spots that were taken witlin days of the vidicon spectrometer run,
allowing
extending
relative
be
obta.ined,
basically
the photometer data for more complete surface coverage.
For example,
planet's
to
reflectivities
Figure 25
shows the
disk during one run.
position of
This
the slit
on
one slit passes through* the
Coprates canyon as well as a large dust storm to the southwest
Coprates.
Using
a photometer
resolution to match the
be forthcoming.
the
spot as a
of
standard and modifying
photometer, some interesting data
should
page 52
MMERET~it
gg
E
MRBS
VIDSPEC B
1 OF 4
OCT. 17, 1973
T= 11:14 UT
LAT= - 17. 2
LONG.= 51.8
DIR 21.47 SEC
Figure 25. Position of one set of spectra across the
disk of Mars. Latitude and longitude of
the sub-earth point, S, .given.
page 53
REFERENCES
J. B. (1968)
Adams,
"Lunar and Martian Surfaces: Petrologic Significance
of Absorption Bands in the Near-Infrared, " Science 159, p. 1453-1455.
Adams,
J. B. and T. B. McCord (1969) "Mars: Interpretation of Spectral
Reflectivity of Light and Dark Regions, " JGR 74, p. 4851-4856.
Crowell, M. H. and E. F. Labuda (1969) "The Silicon Diode Array Camera
Tube, " Bell System Technical Journal, May-June 1969, p. 1481-1528.
Dollfus, A. (1961) "Polarization Studies of Planets, " Chapter 9 in
Planets and Satellites, edited by G. P. Kuiper and B. M. Middlehurst,
(Chicago: University of Chicago Press).
Hovis, W.A. ,Jr. (1965) "Infrared Reflectivity of Iron Oxide Minerals,
Icarus 4, p. 4 2 5 - 4 3 0 .
Kunin,
J. S. (1972)
"A Technique for Two -Dimensional Photoelectronic
Astronomical Imaging, With Application to Lunar Spectral Reflectivity Studies, " M.S. Thesis, M. I. T., September 1972.
McCord, T. B., and J. Bosel. (1973) "Silicon Vidicon Astronomy at MIT,"
presented at the symposium, "Astronomical Observations with
Television-Type Sensors, " held May 15-17, 1973, at the University
of British Columbia.
McCord, T. B. , J. H. Elias, and J. A. Westphal (1971) "Mars: The Spectral
Albedo (0. 3-2. Sp) of Small Bright and Dark Regions, " Icarus 14,
p. 245-251.
McCord, T. B. and J. A. Westphal (1971) "Mars: Narrow-Band Photometry,
from 0. 3 to 2. 5 Microns, of Surface Regions During the 1969
Apparition," Astrophys.J. 168, p. 141-153.
McCord, T. B. and J. A. Westphal (1972) "Two -Dimensional Silicon Vidicon
Astronomical Photometer, " Applied Optics 11, p. 522-526.
Sagan, C. , J. P. Phaneuf, and M. Ihnat (1965) "Total Reflection Spectrophotometry and Thermogravimetric Analysis of Simulated Martian
Surface Materials, " Icarus 4, p. 4 3 - 6 1 .
Tull, R. G. (1966) "The Reflectivity Spectrum of Mars in the Near-Infrared,"
Icarus 5, p.505-514.