62
Devices that use diffusers should also be cleaned daily by gently brushing debris from the diffuser
material. If the diffuser is extremely dirty, distilled water can be used on most diffusers, but other cleaning
chemicals should be avoided. The manufacturer should be consulted on the most appropriate cleaning
m ethods.
The half-angle of spectral radiometers is generally less than half that of pyrheliometers. Therefore,
pointing alignment of these instruments must be checked regularly; even if active-tracking is being
used. Any changes in the alignment of the optical axes of either the radiometer or the active-tracking
sensor can lead to large errors in AOD. Some active-trackers allow for the monitoring of the output
of the active sensor, while a few spectral radiometers have quadrant sensors imbedded in the instrument
that logs the pointing accuracy. Both of these devices can be used to monitor the quality of the pointing.
On systems that combine active-tracking with passive tracking, the system clock should be checked
regularly so that the passive mode points correctly also.
7.6 Archive Information
Data transmitted to the archive will be in the form of spectral transmission at the wavelengths given
in Table 7.1. To calculate AOD from the transmission data, the archive will require information on both
the instrument and the atmosphere at the time of the observation. Table 7.2 summarizes the data required
by the archive to calculate the AOD from the transmission value, while Table 7.3 outlines the instrument
parameters required to understand the measurement.
Parameter Description Comment
Date Date of observation Date in archive format
Time (t) Time of measurement
in seconds of the day
Numeric value from 1 to 86400
Delta Time (*t) Period in seconds to
collect observation set
To be used in calculations and quality assurance of
tim e
Observed Solar
t
Zenith (2 )
Observed solar zenith
angle in radians
To be used in calculations and quality assurance of
tim e
P(t) Actual atm ospheric
pressure (hPa) at tim e
of observation
To be used in calculations. May be submitted
separately with other archived data
3
O Column ozone amount
in atm. cm
To be used in calculations. May be submitted
separately with other archived data. Ozone amount
is to be representative of ozone overburden at
time t
Radiometer
Temperature
Numeric in °C Instrument temperature if thermostatically controlled
or available if not controlled. The ambient
temperature is sufficient for instruments without
temperature control. The latter may be submitted
separately with other archived data
1
Transmission at 8
81
(T )
Direct transmission
Diffuse transmission
1 81
at 8 (D )
Diffuse transmission For cosine style instruments only
1n
Repeat Transmission parameters for each measured wavelength (8 ... 8 )
Table 7.2. Information that is required by the archive to calculate AOD from transmission data.
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Komentáře k této Příručce