Terra. Nova. Bay station in. Antarctica. (74.6°S,. 164.6°E) during the summer expeditions. 1988-1990 of. PNRA. (PNRA is the national research program in.
N95- 11071
OZONE
GROUND-BASED
MEASUREMENTS
G. Giovanelli,
BY
P. Bonasoni,
CNR
-
the
"GASCOD"
M. Cervino,
FISBAT
GASCOD,
a
differential
near-ultraviolet
optical
and
spectrometer,
was
measurements
taken
program di Ricerche coincident in
the
same
visible
area
presented, as is another comparison performed Italy. Also introduced is an updated model solar zenith measurements taken from ground-based, which was campaign 13.1°E)
upward-looking employed for
at Are-Ostersund during EASOE
2.
is in for a
in of
remote the
no knowledge measurement,
calibration without need A DOAS spectrometer Vis spectral regions diode-array sensors a multi-wavelength measurements spectrometer, spectrometer zenith solar
as
made with called correlating radiation,
GASCOD
and
its
data
spectraI dispersion DOAS method for data method in the
values [I] and analysis [4]. remote-sensor
radiation scattered alon E the zenith. spectrometer features a Jobin-Yvon
holographic
spherical
is about detector
cm in length. 0.12 nm/diode O.S run.
the is
grating
The
with
same as the a Hamamatsu
a
input PCD
format: and the
each plxel of array is 2.54
The spectral dispersion and the overall optical
grating
can
be
moved
by
throughput
telescope's. linear diode
is about resolution
a stepper
motor,
and an internal H E lamp is used for wavelength calibration each time the motor moves the gratlng:the spectrum is held to be calibrated only when its two highest values match the position of the array detector's two central
of the unattenuated which is very useful
absorbers with high and high-precision
diodes. spectral
for a reference gas. working in the UV and can use the linear
method
of multiple and specificity
the same the same DOAS
array detector with Ix512 the array is 0.050x2.5 mm
atmospheric sensing. Other advantages DOAS approach include simultaneous
determination sensitivity
of
solar light The GASCOD
that The
regions via differential optical spectroscopy (DOAS). The basic between the differential and absolute methods is that the former, unlike the requires during
description
The very narrow field of view of the input optics (a Cassegraln telescope featurin E 1500 /am focal length and 300 mm diameter) provides the best approximation of the atmospheric transfer equation model for the interpretation of the
A wide range of atmosphere trace Eases, including 03, NO2, OCIO, NO3, BrO, HN02, CH20, S02 and OH can be detected in the UV and visible
latter, spectrum
in laboratory presented and
configuration is used with the atmospheric transfer model to interpret zenith diffuse solar spectrum measurements.
(63.3°N, Arctic
Introduction
spectral absorption difference absorption
F. Ravegnani
ITALY
Stepwise analysis
have use The
Stratospheric Ozone Experiment). The GASCOD can examine the spectra from 300 to 700 nm, in 50 nm steps, by movin E the spectrometer's grating. At present, it takes measurements of solar zenith radiation in the 310-342 nm range for 03 and in the 405-463 nm range for NO2. 1.
SYSTEM
The IX)AS system was developed in two configurations: the GASCOD (fig. l), a groundbased remote sensor for measuring direct and diffuse solar radiation [1, 2], and the l-meter multi-path configuration (fig. 2) to measure absolute gas cross-sections [3]. Both versions
GASCOD spectrometer, the 1991-92 winter in Sweden (European
and
DOAS
developed
in Antarctica, in Antartide"). 03 total column Antarctic
Bologna,
VISIBLE
absorption cross-sections measured by a multi-path spectrometer are discussed.
at CNR's FISBAT Institute in Bologna, Italy, and first tested at Terra Nova Bay station in Antarctica (74.6°S, 164.6°E) during the summer expeditions 1988-1990 of PNRA (PNRA is the national research "Programma Nazionale A comparison with
AND
F. Evangelisti
Institute.
ABSTRACT
NEAR-UV
is I.
a detector, thus becomln E device. The data from
This makes accuracy Our spectral during zenith
based The
on the measurement
spectrum
such a UV/Vis diode-array GASCOD (gas-absorptlon optical differences) for and the 03 dlfferentlal
2.
707
(Is)
The measurement (Io) inferred (solar spectrum or background
it of
possible nm.
to
interpretation solar radiation
following of as
0.2
the
recorded
of from at diffused
the
steps: solar by
ensure
a
of the DOAS measurements zenith the
scattered spectrometer.
sun reference the Langley-plot the top of the solar spectrum
spectrum method atmosphere Ib).
sp l'_rlc_l
mirrors
_¢ Fig.2
Multipoth
Cell Spec_ometer
I,(A)
lo(A)
GASCOD
and
set-up
Is(A)
Laboratory
measurement
of
the
to
"b"
g=0,
cross-sectlons
either
wlth
the
used
identical
in
field
characteristics
or
to
analytical
....
into
followlng
one
having
there
employed
can
Spectral
B.
it
recorded
Smoothing:
It
square
is
the
by
are
cross-sections
applied
to
all Tg
via
non-linear
analysis
(or
in
procedures)
the
absorption
differential
cross-sections
other
values
of
by
regression
D.
Shift
&
subtracting
function
the
from
laboratory-measured applied
to
atmospheric ratio
all
to
their
Regression
so
It
ailgned
as
regression
analysis:
to
features
to
the
(step
of
solar
regression
means
analysis
of
atmosphere
given
in
50
into
minimizing
the
of
the
column
value
residual
regression
of
the
the &
of
the
of
the
can
absorbers'
yield
slant
the
columns.
SOS,
we
used
the
To
procedure
Stretch"whlch
removes
slight
of
spectral
of
I=/-i-_s
in
respect
to
Io/-T_
Intensity-weighted
optical
the
least
to
by
an
gas
is
normally
of
I
account
computation:
to
overcome
model
solar
of
for
radiation
the
the
atmospheric
interpreting
the
zenith
measurements.
atmospheric Air-mass
the
km
only
used
difficulties
transfer
square
parameterizlng
layers
path
narrow
each
the
factor:
vertical
the
it
column
is
computed
amounts
of
to
determine
the
absorbers
and under
taking
slant
spectrum of
linear
applied
equation
the
absorber.
(SOS)
displacement
F. transfer
g-th
I) the
the
zenith
cross-section
by
_R
function.
the
differential analyzed
for and
and
0, I,2,..,n of
calculation being
cross-sectlon scattering),
is
determine
correlation of
=
squares
values
it ratioed
(Mie
least-square
best
£. C.
_o
their
values; the
spectra
g
Stretch:
of
"Shift also
as Rayleigh
the
minimize absolute,
such for
the
of
linear analyzed
resulting
vx particle
abundance
sum belnE
the
non-gas
trace,
cross-sectlon),
with
least
applying
smoothing
gases
Among
several
cross-section
large
(Ring
instrument.
determines
regression
absorption
gas.
steps:
alignment:
spectra
the
g-th
be the
A.
is
the
it.
procedure
the
n
of
scattering), dlvlded
of
computed
procedure,
I,2
(molecular The
values
same _g(A)
spectrometer
smoothed respectively
absolute cross-sectlon
absorptlon
the
ground,
the
I=(A)
point
with
along
the
are
and
via _g(A)
3.
scattered
path
lo(k) F_.I
configurotion
lrradlance
the vertical
_ C Om )uter
investigation.
single In
ground-based
measurement
of
zenith
scattering: scattered Is
Io
Is
be
n
I
Z
Io
the lo(A)
supplies value is
of the
density
after the
gas
several slant
incident at
the
solar top
of
and
_z
where:
is
=
I
the flux
into
of range
the
708
nm 03 for
be
simplified
into
50
The
the
NO2
by
slant
for
layers, used
instead
column
employs
the and
The the
atmospheric
study
amounts
the
dividing
Our
is
range
column
can
of
path.
spherical
present
spectral slant
vertical
summation
flux
value
layers.
the
integral.
310-342
atmosphere,
the
equal
thick;
intensity the
along
divided
km
the
integrating
can
atmosphere
radiation the
flux
calculations
simplifications column
by
radiation
g=1
radiation
calculated
model which
solar
each of the
determination the
amounts.
405-463
run
4OO
3OO
,o o c>
2OO
100
I,*,l,,,t.,,i.,,i,,,i,,,i,,.t 13
17
21
25
29 '1
3
7
11
1989
Ozone the
Terra
Nova
[GASCOD]
x
Terra
Nova
[TOMS]
+
South
Pole
[DOBSON]
..,I,,*l.,.I,.'.l,..I.=,l,,,i,,,i.,,l..,i,=,l,,.i,,.i,,.i
November
Fig.3
•
vertical
some
15
19
23
27
31 I
_,
8
12
column
end
24-
January
amounts area
20
os by
28
1
5
I
December
Antarctic
16
measured
Dobson
by
1990
GASCOD
spectrometer
February
and
at
TOMS
South
in
Pole.
35
30 3.
Data
Comparlson
The
GASCOD
(74.6°S,
was
42
4
Bay
on
1989-90
km
the
of
TOMS
station.
The
between
and,
given acceptable
the
trend
overall
values,
between
The
the
detailed
GASCOD
of and
TOMS
farmer's
values
underestimated: in
76X
of
lack
of
fact
that
first
the
cases
the
is
in
the
linear program,
1991
column
data
those
taken
deployed
297
the
other
201
of
in
figure
of
WODC.
60
km The 5;
and
DUs
by
from
the
distribution
TOMS
of
dotaset
in
differences
figure
3.
the
o
25
DUs)
16X.
here
* z_
A
0
0
This to
the
for
the
upgraded
its was
,o, _1
0
03 at
data too,
during
Bologna
near
Ozone
Data at
sets
are show
z_ C,ASCO0
[Bologna]
and
,_ DOBSON [SPC-VVODC
one
o 1_
Bologna,
Center,
Sestola,
they
0
vertical
spectrometers:
Capofiume
Bologna
0
to MOS
repeated
GASCOD
World
as
computational
the
Dobson
compared here,
of and
the
(Hamamatsu
in
the
Pietro the
analysis GASCOO
the
shows
in
used
between
two
Frequency between
of
(average
was
comparison
by San
Fig.4
in
readlnEs.
device
Italy
recorded
at
station
the in
[RZR311K;K_ (DU)
an
Dobson
attributable
GASCOD
array}
and
March
Kx_ K,x>
systematically
being
detection
diode
KX>
10
03
especially
than
the
the of
(Version
frequency
distribution
the
difference
GASCOD
and
shows
same
at
agreement, rather
Terra
KX KX KX
