Observations
6.1 Observation Shelters
Dobson ozone spectrophotometers are commonly wheeled outside from storage shelters for observations. To minimize temperature changes, the instruments may be covered with thermostatically controlled electric heating blankets and quilted covers.
A preferred procedure, which avoids instrument transport and possible consequent instrument jarring, is to house the spectrophotometers in permanent observing shelters. In the U.S.A., astronomical dome-shelters are used that are rotatable and have hatches that open and allow direct sun, moon and zenith sky observations to be made. Such domes are mounted on concrete pads, insulated, heated, air conditioned and equipped with dehumidifiers in tropical climates. For operating convenience, the spectrophotometers inside the dome shelters are mounted on rotatable pedestals.
In polar regions, spectrophotometers are often housed in well insulated, rectangular, flat-roofed structures equipped with windows that open for sun or moon observations and a roof hatch that opens for zenith sky measurements. The need to open windows in cold climates when making direct sun or moon observations may, however, be avoided by using a periscope, devised by R. A. Olafson, to conduct light from above the roof of the spectrophotometer shelter into the instrument. Specifications for fabricating the periscope are available from the Canadian Atmospheric Environment Service, 4905 Dufferin St., Downsview, Ontario.
6.2 Observations of Total Ozone Amount
6.2.1 Observation Types
AD-wavelength observations on direct sun (AD-DSGQP observations) are fundamental. However, a variety of other kinds of routine observations, listed in Table 2, can be made with the Dobson instrument. The kinds of observations to be made at any time depend on sky conditions, the elevation of the sun, and instrument characteristics. For example, the fundamental AD-DSGQP observations can only be made when the sun is unobscured by clouds and when it is fairly high in the sky (mu is less than 3.0 or Z is less than about 70 degrees). When the elevation of the sun is greater than 80° (Z <10° or mu < 1.015), the instrument's sun director becomes unusable and AD-DSGQP observations cannot be made.
In general, DSGQP type observations should not be made at high mu since at low sun the brightness of the sky in the vicinity of the sun may be comparable in brightness to the sun's disc for short wavelengths. Since skylight has a different spectral composition from sunlight, spectrophotometer readings may be adversely affected. (Also, for A wavelengths, errors due to scattered light within the instrument occur at high mu.) Limiting dial readings for DSGQP type observations may be determined by taking a series of observations on the rising or setting sun, computing the ozone amounts and plotting them against N. At some value of N that should not be exceeded during routine measurements, the ozone amounts will apparently begin to decrease. Focused image (FI) type observations, on the other hand, should not be made on very low sun since errors arise due to light scattering within the instrument. At high mu the intensity of the short wavelength is extremely small compared to that of the long wavelength of each Dobson instrument wavelength pair, and may be comparable to the intensity of spurious light scattered by the instrument's optical surfaces. Finally, ZB and ZC type observations should not be made when the sun is low in the sky since deduced ozone amounts then become unreliable.
Table 2. Possible Types of Total Ozone Observations
Type of Obs. Wavelengths Light Source Observing Range
AD-DSGQP A and D Direct sun, using GQP 1.15 < mu < 3.0 AD-DSGQP* A and D Direct sun, using GQP* 1.015 < mu < 1.15 CD-DSGQP C and D Direct sun, using GQP 2.4 < mu < 3.5 AD-DSFI A and D Focused image of sun 2.5 < mu < 4.0 CD-DSFI C and D Focused image of sun 2.5 < mu < 6.0 AD-ZB A and D Clear zenith 1.15 < mu < 4.0 CD-ZB C and D Clear zenith 1.8 < mu < 5.8 CC'-ZB C and C' Clear zenith 1.0 < mu < 4.4 AD-ZC A and D Cloudy zenith 1.15 < mu < 2.4 CD-ZC C and D Cloudy zenith 1.8 < mu < 5.8 CC'-ZC C and C' Cloudy zenith 1.0 < mu < 4.4 AD-RMFI A and D Focused image of moon 1.15 < mu < 3.0 CD-RMFI C and D Focused image of moon 1.15 < mu < 3.5 D-RMFI D Focused image of moon** 3.0 < mu < 5.0
*[Lens should be removed from the sun director (see Section 6.2.4.1).]
**[This observation made only in polar regions (see Section 7.1).]
6.2.2 Times of Routine Ozone Measurements
Routine total ozone observations should be made each day near local apparent noon (L.A.N.) as well as during "observing windows" defined by the times of occurrence in the morning and afternoon of the mu ranges* specified below:
As seasons progress from summer to winter, one or more of the observing windows approach the time of L.A.N., and should be omitted for approach times shorter than about one-half hour. As indicated in the previous section, an additional constraint on making observations is that direct sun observations are not possible for mu <1.015 since with the sun overhead, the spectrophotometer's sun director becomes unusable. Also, with high sun ozone observations made on the zenith sky become unreliable.
*[Observations during 3.5 At stations where
a regular schedule of observations must be followed throughout the year, or
at very high latitude stations where mu changes slowly with time, it is less
satisfactory but acceptable to make observations at L.A.N., and in the mornings
and afternoons at times symmetrical about L.A.N. and spaced two to four hours
apart in time. The reason that exact observing times may not be specified
is that an observer may not be available to make observations at regular times
because of other pressing work that he might be required to do. Furthermore,
he may wish to advance or retard the time of an observation in order to make
more precise measurements on, say, direct sun or clear sky, rather than on
cloud.
To ensure that observers
do not waste their time in making total ozone measurements which cannot yield
usable data, it is useful to provide each ozone observing station with a table
entitled Times of Routine Measurements of Total Ozone Amount. This
table, a sample of which is shown in Table 3,
lists the approximate time intervals during daylight hours when various types
of ozone observations may be made and classifies the different observations
according to priority. Note that AD-DSGQP measurements are most reliable and
should be made whenever possible. They are, therefore, assigned a priority
1. Other types of observations should be made in accordance with listed priorities.
An observer should always consult his Times of Routine Measurements of
Total Ozone Amount table before making an ozone measurement in order to
determine what type of observation to make.
Alternatively, computer
produced mu tables (for every minute of each day) may be provided to field
stations to aid observers in planning their observation programs. Such tables
are especially useful where reduction of observational data is performed on
site.
AD-RMFI and CD-RMFI
observations should be made in polar regions on the one-half full to full
moon every two to three hours whenever adequate instrument sensitivity exists.
In lower latitude regions, moon observations need not be made whenever reliable
direct sun or zenith sky data are obtained, except when special investigations
are undertaken. Moon observations on AD wavelengths are preferred. In general,
it is found that CD-RMFI observations can be made on full moon with a sensitive
spectrophotometer down to mu ~ 4.5 when the total amount of ozone is low.
Useful moon observations in polar regions can also be made on D wavelengths
alone.
6.2.3 Recording Observational Data
The spectrophotometer
dial readings, as well as other pertinent information, should be recorded
on a form similar to that shown in Figure 4. Computations
of mu and the total ozone amount are made directly on the form.
Under Notes indicate
the condition of the sky at the time of observation according to the following
code:
(b) Cloudy sky (when making zenith observations only):
L - Low TN - Thin U - Uniform M - Middle M - Medium V - Variable H -
High TK - Thick P - Patchy
6.2.4 Observing Methods
This section outlines
in detail procedures to be followed in making various types of total ozone
measurements. Note that AD-DSGQP observations are fundamental; other types
of measurements are made similarly, with minor variations.
Regardless of the
type of observations to be made, the ozone spectrophotometer should be prepared
for use by executing operations (1) to (5) given below. Failure to perform
these operations in the order presented may result in damage to the microammeter
or photomultiplier.
(2) Check to ensure that the microammeter shunt is in the position of
least microammeter sensitivity.
(3) Check to ensure that the photomultiplier step switch is positioned
at step 1, the position of least photomultiplier sensitivity.
(4) Turn on the spectrophotometer power supplies.
(5) Install a newly smoked plate (or waxed chart) on the spectrophotometer
R-dial and wind the recording mechanism clock.
6.2.4.1 AD-DSGQP Observations
(2) Uncover the spectrophotometer inlet window and place the ground quartz
plate over it.
(3) Place the sun director over the inlet window. The lens* within the
sun director must be in its lowest position. IMPORTANT: When using
the sun director, make certain that a tube within the unit that prevents
sky light from entering the sun director through slots in its sides is in
position; otherwise an appreciable amount of sky light may enter the instrument
causing erroneous readings, especially when direct sun observations are
made on low sun. For this reason, also, the ground quartz plate viewinq
window built into the sun director must always be closed when observations
are being made.
*[The purpose of the lens is to increase available light intensity and,
hence, instrument sensitivity at low sun (mu ~ 3), and to permit focused
image observations to be made. For Dobson instruments equipped with sensitive
photomultipliers and electronics, and where, also, focused image observations
are not made, use of the lens within the sun director may be omitted. Since,
however, differential absorption of light at the A, B, C, and D wavelengths
can occur within the lens depending on the optical quality of the quartz
from which it is made, care must be taken to determine any differences in
N values that may arise when observations are made with and without the
lens. Appropriate corrections must then be applied when processing observational
data.]
(4) Insert the S4 shutter rod all the
way into the spectrophotometer. Set the wavelength selector rod to the SHORT
position.
(5) Read the temperature of the instrument to the nearest 0.5 degree Celsius
and set the Q1 lever stops for A and D
wavelengths according to values given in the Table of Settings of Q.
The Q2 lever stops are always set to the
values given in the table corresponding to the temperature of 15° C.
(6) Orientate the instrument so that its long axis points toward the sun,
the sun being on the observer's right hand. (It is important to align the
spectrophotometer carefully with respect to the sun; otherwise, errors may
result in the measurement. If several observations are made in succession,
the orientation of the instrument should be periodically checked and corrected.)
(7) Switch on the motor which drives the sector wheel.
(8) Adjust the prism of the sun director so that the patch of sunlight
falls centrally on the ground quartz plate.
(9) Set Q1 and Q2
levers for A wavelengths and increase microammeter sensitivity by rotating
the shunt potentiometer fully clockwise. There should now be a small deflection
of the microammeter. Turn the R-dial to bring the microammeter reading to
zero and gradually increase the photomultiplier voltage with the step switch,
if necessary, until sufficient sensitivity is obtained as indicated by a
slight instability of the microammeter needle. Make a mental note of the
position of the step switch.
(10) Rotate the step switch to step 1 to reduce the voltage on the photomultiplier
and set Q1 and Q2
levers for D wavelengths. As in step (9), increase the photomultiplier voltage
while zeroing the microammeter until suitable sensitivity is obtained. Again,
note the setting of the step switch controlling sensitivity and the approximate
R-dial reading.
The spectrophotometer
has now been readied for use in making an AD-DSGQP observation. Take actual
observations as follows:
(12) Since it is always good practice to commence an observation at the
beginning of a minute, glance at your chronometer (or other timepiece giving
accurate time) and either make a mental note of the time you will begin
the observation or record that time on a scratch pad. (To preserve accuracy
in computed data, observations must be timed to within ±10 seconds of correct
time when the sun is rising or setting fairly rapidly.)
(13) Several seconds before starting time, set the patch of sunlight centrally
on the ground quartz plate. The patch of sunlight will shift during the
course of the observation, and will require readjustment (see step (19)).
(14) At starting time, lower the recorder stylus on to the smoked plate.
(15) Carefully and slowly oscillate the R-dial so that the microammeter
needle deflects just to one side of zero, then just to the other side, etc.
Continue the manipulation of the R-dial for 20 seconds.
(16) Reduce sensitivity to that suitable for D wavelengths. Raise the
stylus off the smoked plate.
(17) Set Q1 and Q2
levers for D wavelengths while at the same time adjusting the R-dial to
the reading expected (see operation (10)).
(18) Lower the stylus again and record the R-dial reading for 20 seconds
as in (15).
(19) Raise the stylus off the smoked plate. Set Q1
and Q2 levers for A wavelengths while
rotating the R-dial to its correct position. Adjust the step switch for
suitable sensitivity. Lower the stylus and again and make a 20 second recording
of the R-dial reading. Adjust the sun director, if necessary, so that the
patch of light falls centrally on the GQP.
(20) Repeat operations (16) to (19). You will now have completed an ADADA
observation. Glance at the chronometer and record on a scratch pad the time,
in hours, minutes, and seconds, when the observation was completed.
(21) To shut down the spectrophotometer, first set the sensitivity step
switch to step 1. Then, decrease the microammeter sensitivity to zero by
turning the shunt potentiometer. Finally, switch off the sector wheel motor
and power supplies, remove the sun director, and replace the cover over
the inlet window.
(22) Carefully bisect the traces made on the smoked plate with the stylus
and read mean values of the traces to the nearest 0.1 degree. Record the
dial readings, mean observing times, and other pertinent information.
6.2.4.2 AD-DSGQP* Observations
Observations of this
type are made only when the sun is very high in the sky, i.e., 1.015 6.2.4.3 CD-DSGQP Observations
These observations
are made in the same way that AD-DSGQP measurements are made, except that
the Q1 and Q2
lever stops are set for C and D wavelengths.
6.2.4.4 AD-ZB Observations
AD-ZB measurements
are made on a 7-degree cone of light emanating from the zenith sky. The observing
procedure is the same as for AD-DSGQP measurements except that the sun director
and ground quartz plate are not used. (DO NOT USE THE GROUND QUARTZ PLATE).
Care must be taken during the measurement to ensure that the cone of light
entering the spectrophotometer is unobstructed by centering the instrument
accurately beneath the observatory hatch if observations are made from within
a building.
6.2.4.5 AD-ZC Observations
AD-ZC and AD-ZB observations
are made in exactly the same way. For accuracy, it is necessary to make the
A and D measurements on a very similar cloud; hence, a close watch must be
maintained on the zenith sky during observations. If measurements must be
made on variable or patchy cloud, two or three observations of the type ADADA
should be made in succession, to constitute a single ozone determination.
AD-ZC measurements
can also be made when light rain or snow is falling if the spectrophotometer
is housed in an observing shelter. A fan mounted beside the observatory hatch
can be used to blow raindrops or snowflakes away from the spectrophotometer
inlet window during observations.
6.2.4.6 CD-ZB and CD-ZC Observations
These observations
are made in the same way that AD-ZB and AD-ZC measurements are made. except
that the Q1 and Q2
stops are set for C and D wavelengths. The observation are made in the mu-range
1.8 to 5.8, and are useful primarily at high latitude stations at times of
the year when the sun is low in the sky.
6.2.4.7 CC'-ZB and CC'-ZC Observations
These observations
are made in the same way that AD-ZB and AD-ZC measurements are made, except
that the Q levers are set for C wavelengths and maintained in that position.
The sequence of observations is CC'CC'C. Observations on C wavelengths are
made with the wavelength selector rod in the SHORT position whereas observations
on C' wavelengths are made with this rod in the LONG position. The S4
shutter rod should be set all the way into the spectrophotometer and maintained
in that position throughout the observations. As in the case of AD-ZC measurements,
care should be taken to see that the C and C' readings are made on closely
similar cloud. If measurements must be made on variable or patchy cloud, two
or three observations should be made in succession to constitute a single
ozone observation.
6.2.4.8 AD-DSFI and CD-DSFI Observations
AD-DSFI and CD-DSFI
measurements are similar to AD-DSGQP and CD-DSGQP measurements, respectively,
except that the ground quartz plate is not employed and a focused image of
the sun is cast on slit S1 by the sun director.
A mark is made on the side of the sun director showing the correct position
of the lens at which a sharp image of the sun is thrown on S1
at wavelengths of about 3200 A.U. If such a mark has not been made, it can
be made as follows. Using a green filter, find the lens position on the sun-director
when a sharp image of the sun is formed on S1.
The position for a sharp focus at 3200 A.U. will be 15 mm below that for green
light.
Since it is not possible
to see slit S1 easily through the viewing
hole at the bottom of the sun director, a small glass viewing prism is fitted
under the main quartz prism. Also, small marks are inscribed on the jaws of
the slit which permit the positioning of the sun's image approximately centrally
along the length of the slit. It will be found that if the sun's image is
moved along the length of the slit, the dial readings will change, but it
will generally be found that there is some region near the center when a small
movement of the image along the slit makes little difference in dial readings.
Tests should be made to find this position, and the sun's image should always
be set at this point during observations.
It is necessary to
set the sun's image very carefully on the slit and allow for the movement
of the sun so that the slit will bisect the sun's image halfway through the
observation. A preliminary test must be made to see how much the sun's image
moves in, say, 20 seconds. The observation should not be continued for more
than 30 seconds without resetting the sun's image on the slit, unless a second
observer is present to keep the sun's image continuously in the center of
the slit.
There is a great difference
in the intensity of light at the C and D wavelengths when the sun is low.
After the observation on C wavelengths has been made, the instrument sensitivity
must be greatly reduced before changing to D wavelengths. Often the
sensitivity at the D wavelengths is too great even with the lowest voltage
on the photomultiplier, and the voltage output of the photomultiplier power
supply must then be reduced.
At least three independent
ADADA or CDCDC observations should be made in succession.
WARNING! In order
not to damage the photomultiplier, DSFI observations should not be made when
the sun is high in the sky (mu <2.5).
6.2.4.9 AD-RMFI and CD-RMFI Observations
These observations
are made in a manner similar to AD-DSFI and CD-DSFI measurements except that
the one-half full to full moon is used as a light source.
At low latitude stations
when the moon is nearly overhead, a satisfactory image of the moon will not
be projected onto slit S1 by the sun-director
(a skewed image will result because of the oblique angle at which the rays
of moonlight strike the face of the sun-director prism). To view a proper
image, a moon-director prism unit is provided with each spectrophotometer
for attachment to the sun-director whenever observations on high moon are
made.
6.3 Umkehr Observations
Umkehr observations
yield highly useful information on the vertical distribution of ozone in the
atmosphere. Two types of Umkehr observations are possible. The first involves
a standard Umkehr observing procedure (Mateer and Dütsch, 1964) that has been
in use since the late 1950's, while the second is a newly developed short
method (Mateer et al., 1979) which has a time saving advantage that allows
for an increased frequency of such observations to be made during conditions
of clear sky and relatively constant total ozone amount. Every effort should
be made by observers to make short Umkehr measurements whenever sky conditions
permit. Additionally, coincident standard Umkehr observations should be made
whenever possible in order that a large amount of data become available for
comparing ozone vertical distributions derived from the two observing methods.
A standard Umkehr
observation consists of a series of C-wavelength measurements made on the
clear zenith sky during morning or afternoon. The measurements are commenced
a few minutes before sunrise and continued until the sun is at an elevation
of not less than about 20 degrees, or commenced in the afternoon when the
sun is at an elevation of not less than about 20 degrees and continued until
shortly after sunset. A short Umkehr observation, on-the-other-hand, is comprised
of clear zenith sky observations on A, C, and D wavelengths during morning
or afternoon when the sun is at an elevation of from 0 to 10 degrees. The
zenith sky must be free from clouds for a period of from one-half to one hour
near sunrise or sunset to make Umkehr observations. This is especially true
at low latitude stations where the sun rises or sets rapidly. At other times,
it is desirable that the zenith sky be cloudless but permissible that clouds
cross it periodically when measurements are not made. Umkehr observations
cannot be made at a polar station, or at high latitude stations during summertime
when the sun does not sink below the horizon.
To be able to compute
the vertical distribution of ozone, it is necessary to know the total amount
of ozone present at the time of observations. Several total ozone measurements
must, therefore, be made during the morning or afternoon, particularly if
the ozone amount is changing fairly rapidly. The measurements should include
an ozone observation at mu ~ 3.0.
6.3.1 Observing Times
Standard Umkehr measurements
involve the determination of values of NC
when the sun is at discreet positions in the sky, namely, when Z is 60, 65,
70, 74, 75, 77, 80, 83, 84, 85, 86.5, 88, 89, and 90 degrees. Short Umkehr
observations involve determinations of values of NA,
NC, and ND
when Z is 80, 83, 85, 86.5, 88, and 89 degrees. It is convenient to prepare
tables (see sample Table 4) showing the approximate
times during the year at a particular station when specified solar zenith
angles occur. Note that the times listed in Table
4 are only approximate. Their purpose is to aid the observer in effectively
planning his schedule of observations. The approximate times are also useful
when hand computations are performed (see Section 4,
Appendix F) to obtain the exact times during any one-half day when
the sun is at 60, 65, 70 degrees, etc.
It is generally not
sufficient to make only one observation at each specified Umkehr zenith angle.
Rather, several measurements should be made in order to achieve high measurement
precision.
Table 4 MORNING UMKEHR OBSERVATIONS
Date Z 90° 89° 88° 86.5° 85° 83° 80° 77° 74° 70° 65° 60° LAN
6.3.2 Recording Observational Data
The dial readings
and times at which the various measurements are made should be entered on
a form similar to that shown in Figure 5. The
times entered should be correct to within ±5 seconds. Under Notes indicate
the condition of the zenith sky at the time of each observation.
6.3.3 Observing Procedures
A short Umkehr observation
is made on A, C, and D wavelengths. Observations should be made continuously
when the sun is rising or setting rapidly near sunrise or sunset (i.e., when
Z is greater than about 78 degrees). One procedure is to obtain a 20 second
record of an observation on A wavelengths, beginning the recording 10 second
before the minute. Quickly determine the RA
value and record it together with the time of observation, adjust instrument
controls for C wavelength observations, and commence an observation on C wavelengths
beginning 10 s before the next minute. Proceed similarly to obtain a D wavelength
observation beginning 10 s before the third minute. Repeat the sequence, beginning
10 s before the fourth minute, etc.
For solar zenith angles
less than about 78 degrees, observations on A and D wavelengths should be
discontinued, but continued using C wavelengths in order to obtain standard
Umkehr data. As soon as the sun's rate of ascent or descent has diminished,
the frequency of C-wavelength observations may be reduced to once per 2 minutes
and later to once per 5 to 10 minutes. (Alternatively, measurements may then
be made at one minute intervals about the Z times of interest only, starting
2 or 3 minutes before a particular occurs and ending 5 or 6 minutes later).
6.4 Special Observations
6.4.1 Observations Made to Check the Spectrophotometer
Calibration at A, C, and D Wavelengths
The measurements consist
of the usual AD-DSGQP and CD-DSGQP observations made during a one-half day
when meteorological conditions are stable (i.e., when the total ozone amount
is not changing) and the sky is relatively free from dust, smoke, and haze
particles. Since a clear sky and stable meteorological conditions may occur
relatively rarely, it is recommended that the special observations be made
as often as possible.
Observations must
be made twice per one-half day, at a time when the sun is fairly low in the
sky (2.5 Record the data in
the same manner that routine total ozone observational data are recorded.
The method of analyzing the data to check on the calibration state of the
spectrophotometer is described in Appendix D.
6.4.2 Observations Made to Correct Empirical Charts
Each ozone observatory
should be provided with zenith sky Charts AD, CD, and
C; a Chart of Cloud Corrections for Chart C; and a Table
of Cloud Corrections for Chart AD. The charts and the table are used in
deducing total ozone amounts from measurements made on the clear and cloudy
zenith sky.
The charts and table
supplied to a newly set up station will require some modification to suit
the locality where the observations are made, since the vertical distribution
of ozone as well as the ground albedo may be different at the new station
from the ozone distribution and albedo at the station where the charts and
table were drawn up. Furthermore, it may be necessary to affix ordinate or
abscissa values to the charts. At an already established station, improved
corrections to the charts may be required. All original computations of ozone
determined from zenith sky measurements should therefore be regarded as provisional.
The observer should make every effort to accumulate a sufficiently large body
of direct sun and zenith sky comparison data which will enable him to modify
his charts and table appropriately.
Since AD-DSGQP observations
are fundamental, the types of quasi-simultaneous comparisonmeasurements to
be made are the following: Note that the first three sets of the above observations can usually be
made within a few minutes of each other. Direct sun and zenith cloud measurements,
on the other hand, may often have to be 1 or 2 hours apart in time. Each comparison
should consist of at least two independent observations made on direct sun
followed by at least two independent measurements made on the clear or cloudy
sky. Observations should be made over as wide an X and mu range as possible
so that sufficient data become available for correction of the charts and
table.
6.4.3 Determination of Focused Image Corrections
It is generally found
that ozone values deduced from measurements made on direct sun using a ground
quartz plate differ from quasi-simultaneous values determined from focused
image observations. In the case of single pair wavelengths, the differences
may be very large and allowances must be made for them. The differences for
double pair wavelengths, e.g., the CD wavelengths, are usually small and may
even be negligible.
6.4.4 Multiplying Factors Used in Reducing CD-DSGQP Values
to the AD-DSGQP Level
The ozone absorption
coefficients incorporated into equations (3) to (7) given in Section
7.1 are the 1968 IAMAP (International Association of Meteorology and Atmospheric
Physics) coefficients adopted for use with Dobson spectrophotometers at the
recommendation of the International Ozone Commission (IOC). When quasi-simultaneous
ozone measurements are made on direct sun or moon using AD and CD wavelengths,
it may be found that each type of measurement gives a slightly different result.
Such differences are due to uncertainties in the ozone absorption coefficients
employed in reducing the data, as well as instrumental factors and observing
conditions (e.g., atmospheric aerosol loading). For- all ozone values to be
comparable, it is necessary to determine multiplying factors to ozone values
deduced from measurements on CD wavelengths by which results may be reduced
to the AD-DSGQP level. The multiplying factors XAD/XCD
are derived from a large number of quasi-simultaneous observations covering
a broad range of mu. Generally, it is found that CD-DSGQP values do not differ
from AD-DSGQP values by more than 2%.
Return to Table of Contents
Forward to Section 7. Reduction of Ozone Data
TIMES OF ROUTINE MEASUREMENTS OF TOTAL OZONE AMOUNT
(Observing Time Intervals in E.S.T.)
Type Obs.
Priority
mu-rangeDirect Sun Observations
Clear Zenith Observations
Cloudy Zenith Observations
AD-DSGQP
1
(1.15 < mu < 3.00)AD-DSGQP*
1a
(1.015 < mu < 1.15)CD-DSGQP
2
(2.40 < mu < 3.50)CD-DSFI
3
(3.00 < mu < 6.00)AD-ZB
4
(1.15 < mu < 4.00)CC'-ZB
5
(1.00 < mu < 4.40)AD-ZC
6
(1.15 < mu < 2.40)CC'-ZC
7
(1.00 < mu < 4.40)
Jan. 1
6
11
16
210945-1443
0943-1443
0940-1456
0936-1504
0931-1512
0920-1039
0919-1035
0917-1030
0913-1023
0909-10151348-1507
1357-1513
1406-1519
1417-1527
1428-15340826-0945
0826-0943
0824-0940
0822-0936
0819-09311443-1601
1449-1606
1456-1612
1504-1618
1512-16210903-1524
0902-1530
0900-1536
0857-1542
0853-1550
0853-1535
0852-1540
0850-1546
0848-1552
0844-15591039-1348
1035-1357
1030-1406
1023-1417
1015-1428
0853-1535
0852-1540
0850-1546
0848-1552
0844-1559
26
31
Feb. 5
10
150925-1521
0918-1530
0910-1538
0902-1547
0854-1555
0903-1007
0857-0958
0851-0948
0843-0939
0836-09291439-1452
1450-1550
1500-1558
1510-1605
1520-16130815-0925
0810-0918
0804-0910
0758-0902
0752-08541521-1631
1530-1637
1538-1644
1547-1651
1555-16570849-1557
0843-1604
0837-1612
0830-1619
0822-1626
0839-1606
0834-1613
0828-1621
0821-1628
0814-16351007-1439
0958-1450
0948-1500
0939-1510
0929-1520
0839-1606
0834-1613
0828-1621
0821-1628
0814-1635
20
25
Mar. 2
7
120847-1602
0837-1610
0828-1617
0819-1624
0810-1630
0828-0919
0819-0909
0811-0859
0802-0849
0754-08391529-1620
1537-1627
1546-1634
1553-1640
1600-16460745-0845
0737-0837
0730-0828
0721-0819
0713-08101602-1703
1610-1709
1617-1715
1624-1721
1630-17260815-1633
0807-1640
0759-1646
0750-1652
0742-1658
0806-1641
0759-1648
0751-1654
0742-1700
0734-17060919-1529
0909-1537
0859-1546
0849-1553
0839-1600
0806-1641
0759-1648
0751-1654
0742-1700
0734-1706
17
22
27
Apr. 1
60810-1636
0753-1641
0744-1647
0736-1652
0728-1656
0745-0830
0737-0821
0729-0812
0721-0804
0713-07561607-1652
1613-1657
1618-1702
1624-1707
1629-17120705-0801
0657-0753
0649-0744
0642-0736
0634-07281636-1732
1641-1737
1647-1742
1652-1746
1656-17510733-1704
0725-1709
0717-1719
0709-1719
0702-1723
0729-1711
0718-1716
0710-1721
0702-1726
0654-17310830-1607
0821-1613
0812-1618
0804-1624
0756-1629
0726-1711
0718-1716
0710-1721
0702-1726
0654-1731
11
16
21
26
May 1
0721-1211
0715-1142
0708-1112
0701-1057
0656-1046
1211-1701
1238-1705
1315-1710
1318-1714
1328-1718
1211-1211
1142-1238
1112-1315
1057-1318
1046-13280706-0748
0659-0741
0652-0735
0646-0729
0641-07231634-1716
1638-1721
1643-1725
1647-1729
1651-17340627-0721
0620-0714
0613-0708
0607-0701
0601-06561701-1756
1706-1800
1710-1805
1714-1809
1718-18130654-1211
0647-1135
0641-1112
0635-1057
0629-10461211-1728
1244-1732
1305-1737
1318-1741
1328-17450647-1735
0640-1740
0633-1744
0627-1748
0622-17530748-1211
0741-1135
0735-1112
0729-1057
0723-10461211-1634
1244-1638
1305-1643
1318-1647
1328-16510647-1735
0640-1740
0633-1744
0627-1748
0622-1753
6
11
16
21
260651-1037
0647-1029
0643-1024
0640-1019
0637-10161336-1722
1343-1726
1349-1730
1354-1733
1358-17361037-1336
1029-1343
1024-1349
1019-1354
1016-13580636-0718
0631-0714
0627-0710
0624-0707
0622-07051655-1738
1659-1742
1702-1745
1706-1749
1709-17520556-0651
0551-0647
0547-0643
0544-0640
0541-06371722-1818
1726-1822
1730-1826
1733-1830
1736-18330624-1037
0619-1029
0616-1024
0612-1019
0610-10161336-1749
1343-1753
1349-1757
1354-1801
1358-18040616-1757
0612-1801
0608-1805
0605-1808
0602-18120718-1037
0714-1029
0710-1024
0707-1019
0705-10161336-1655
1343-1659
1349-1702
1354-1706
1358-17090616-1757
0612-1801
0608-1805
0605-1808
0602-1812
31
June 5
10
15
200636-1013
0635-1012
0634-1011
0634-1011
0635-10121402-1739
1405-1742
1409-1746
1409-1746
1411-17481013-1402
1012-1405
1011-1407
1011-1409
1012-14110620-0703
0619-0702
0618-0702
0618-0702
0619-07031712-1755
1714-1758
1717-1800
1718-1802
1720-18040539-0636
0537-0635
0537-0634
0537-0634
0537-06341739-1836
1742-1839
1744-1842
1746-1844
1748-18450608-1013
0607-1012
0606-1011
0606-1011
0607-10121402-1807
1405-1405
1407-1812
1409-1814
1411-18160600-1815
0559-1818
0558-1820
0558-1822
0559-18240703-1013
0702-1012
0702-1011
0702-1011
0703-10121402-1712
1405-1714
1407-1717
1409-1718
1411-17200600-1815
0559-1818
0558-1820
0558-1822
0559-1824
25
30
July 50636-1013
0638-1015
0640-10171412-1749
1412-1749
1411-17481013-1412
1015-1412
1017-14110620-0704
0622-0706
0624-07081721-1805
1721-1805
1721-18040539-0636
0540-0638
0543-06401749-1846
1749-1846
1748-18460608-1014
0610-1015
0612-10171412-1817
1412-1817
1411-18160600-1824
0602-1825
0604-18240704-1013
0706-1015
0708-10171412-1721
1412-1721
1411-17210600-1824
0602-1825
0604-1824
*Remove lens from sun director before making this observation.
(a) Cloudless sky in the vicinity of sun, moon, or zenith:
C - Clear H - Hazy VH - Very hazy
Cloud Height Cloud Thickness Cloud Texture
(1) Unclamp the microammeter movement and zero the microammeter,
if necessary.
(1) Perform operations (1) to (5) given above.
(11) Set Q1 and Q2
levers for A wavelengths and rotate the step switch to give suitable sensitivity
as previously determined.
(Approximate Times of Observation, E.S.T.)
Station: Sterling, Virginia
Jan. 1 0734 0740 0746 0755 0804 0817 0837 0858 0921 0954 1050 1214
6 0734 0740 0746 0755 0804 0817 0837 0857 0920 0953 1045 1216
11 0733 0739 0745 0754 0803 0816 0835 0856 0917 0949 1039 1218
16 0732 0738 0743 0752 0801 0814 0833 0853 0914 0945 1032 1202 1220
21 0729 0735 0741 0750 0759 0811 0829 0849 0909 0939 1023 1131 1221
26 0726 0732 0737 0746 0755 0807 0825 0844 0904 0933 1014 1111 1223
31 0722 0728 0733 0742 0750 0802 0820 0838 0858 0925 1005 1055 1223
Feb. 5 0717 0723 0728 0737 0745 0757 0814 0832 0851 0918 0955 1040 1224
10 0712 0717 0723 0731 0739 0751 0808 0825 0844 0909 0945 1026 1224
15 0706 0711 0717 0725 0733 0744 0801 0818 0836 0901 0934 1013 1224
20 0700 0705 0710 0718 0726 0737 0754 0811 0828 0852 0924 1000 1224
25 0653 0658 0703 0711 0719 0730 0746 0803 0820 0843 0914 0948 1223
Mar. 2 0646 0651 0656 0704 0712 0722 0738 0755 0811 0834 0904 0936 1222
7 0638 0643 0648 0656 0704 0714 0730 0746 0802 0825 0854 0925 1221
12 0630 0635 0640 0648 0656 0706 0722 0738 0754 0816 0844 0914 1220
17 0622 0627 0633 0640 0648 0658 0714 0730 0746 0807 0835 0903 1218
22 0614 0620 0625 0632 0640 0650 0706 0721 0737 0758 0826 0854 1217
27 0607 0612 0617 0624 0632 0642 0658 0713 0729 0750 0317 0844 1215
Apr. 1 0559 0604 0609 0617 0624 0635 0650 0706 0721 0742 0808 0835 1214
6 0551 0556 0601 0609 0617 0627 0643 0658 0713 0734 0800 0827 1212
11 0543 0549 0554 0602 0609 0620 0635 0651 0706 0727 0753 0819 1211
16 0536 0541 0547 0554 0602 0613 0628 0644 0659 0720 0746 0812 1210
21 0529 0534 0540 0548 0556 0606 0622 0637 0653 0713 0739 0805 1208
26 0523 0528 0533 0541 0549 0600 0615 0631 0647 0707 0733 0759 1208
May 1 0516 0522 0527 0535 0543 0554 0610 0625 0641 0702 0727 0753 1207
6 0511 0516 0522 0530 0538 0549 0605 0620 0636 0657 0722 0748 1206
11 0505 0511 0517 0525 0533 0544 0600 0616 0632 0652 0718 0744 1206
16 0501 0507 0512 0520 0529 0540 0556 0612 0628 0649 0715 0740 1206
21 0457 0503 0508 0517 0525 0536 0553 0609 0625 0646 0712 0737 1206
26 0454 0500 0505 0514 0522 0533 0550 0606 0622 0643 0709 0735 1207
31 0451 0457 0503 0512 0520 0531 0548 0604 0620 0642 0708 0734 1207
June 5 0450 0456 0501 0510 0519 0530 0547 0603 0619 0640 0707 0733 1208
10 0449 0455 0501 0509 0518 0529 0546 0602 0619 0640 0706 0732 1209
15 0449 0455 0500 0509 0518 0529 0546 0602 0619 0640 0707 0733 1210
20 0449 0455 0501 0510 0518 0530 0547 0603 0619 0641 0707 0733 1211
25 0450 0456 0502 0511 0520 0531 0548 0604 0621 0642 0709 0735 1212
30 0452 0458 0504 0513 0522 0533 0550 0606 0622 0544 0710 0736 1213
July 5 0455 0501 0507 0515 0524 0535 0552 0608 0625 0646 0712 0738 1214
10 0458 0504 0510 0518 0527 0538 0555 0611 0627 0548 0715 0741 1215
15 0501 0507 0513 0522 0530 0541 0558 0614 0630 0651 0717 0743 1216
20 0505 0511 0517 0525 0534 0545 0601 0617 0633 0654 0720 0746 1216
25 0509 0515 0521 0529 0537 0548 0605 0621 0637 0658 0723 0749 1216
30 0514 0519 0525 0533 0541 0552 0608 0624 0640 0701 0727 0753 1216
Aug. 4 0518 0523 0529 0537 0545 0556 0612 0628 0644 0704 0730 0756 1216
RECORD OF UMKEHR OBSERVATIONS
STN.
INST. NO.
DATE
GMT
RA
Notes
GMT
RC
Notes
GMT
RD
Notes
AD-DSGQP vs. CD-ZB
AD-DSGQP vs. CC'-ZB
AD-DSGQP vs. AD-ZC
AD-DSGQP vs. CD-ZC
AD-DSGQP vs. CC'-ZC .