spring—for more than 10 h a day and only for measurements which were carried
out before the defined summer. Such an approach resulted in a reduced number of
data. We use data from only spring and summer months. Secondly, only clear sky
conditions enable to make any solar measurements and thus the number of “good”
measurement days is also limited.
The AERONET protocols impose standardization of instruments, data quality,
processing and calibration (Holben et al. 1998). The measurements are acquired
with Cimel sun photometer CE-318. This automatic sun and sky radiometer has
spectral interference filters centered at selected wavelengths: 340, 380, 440, 500,
670, 870, 1020 and 1640 nm. The real time operation of the data acquisition and
motion steering are controlled by microprocessors. Sequence of the measurements
is provided automatically every clear day, every 15 min (Holben et al. 1998). The
data accuracy is 0.01 (visible solar radiation) or 0.02 (ultraviolet) (Smirnov et al.
2000). The AERONET provides tree levels of data: level 1.0 (raw data), level 1.5
(cloud-screened data) and level 2.0 (quality-assured data). For the detailed
description see AERONET website (http://aeronet.gsfc.nasa.gov/).
The IOPAN based data obtained with a Microtops II sun photometer were
collected and processed with the pre- and post-field calibration, automatic cloud
clearing and were manually inspected. These portable instruments made by Solar
Light Company are capable of measuring the total ozone column, total precipitable
water vapor and aerosol optical depth (Morys et al. 2001; Ichoku et al. 2002). Each
of these parameters is automatically derived by the instrument from equations
installed by the manufacturer. The Microtops II instruments currently in use at the
IOPAN have five channels, but they may have one of two configurations: 340, 440,
675, 870, 936 nm or 440, 500, 675, 870, and 936 nm. The estimates of uncertainty
of the AOD in each channel oscillates around 0.02. Detailed instrument description
is available at the AERONET webpage (http://aeronet.gsfc.nasa.gov) and has been
presented by Markowicz et al. (2012) and Zawadzka et al. (2014).
In this paper, we also used the data from Koldeway Station in Ny-Alesund
performed by AWIPEV. Data from 2000 until 2012 were obtained using a fullautomatic sun photometer type SP1A produced by Dr. Schulz and Partner GmBH.
The instrument covers a spectral range from 350 to 1,050 nm in 17 channels. It
automatically tracks the sun, which ensures continuity of the measurements. The
AOD uncertainty is 0.01 (Toledano et al. 2012).
3 Methodology
The AOD is a key parameter in aerosol studies which describes the entire atmospheric column and is derived from the Beer-Bouger-Lambert law. In case of Cimel
and SP1A sun photometers the AOD is obtained using the following algorithm.
Annual Changes of Aerosol Optical Depth and Ångström Exponent …
27
out before the defined summer. Such an approach resulted in a reduced number of
data. We use data from only spring and summer months. Secondly, only clear sky
conditions enable to make any solar measurements and thus the number of “good”
measurement days is also limited.
The AERONET protocols impose standardization of instruments, data quality,
processing and calibration (Holben et al. 1998). The measurements are acquired
with Cimel sun photometer CE-318. This automatic sun and sky radiometer has
spectral interference filters centered at selected wavelengths: 340, 380, 440, 500,
670, 870, 1020 and 1640 nm. The real time operation of the data acquisition and
motion steering are controlled by microprocessors. Sequence of the measurements
is provided automatically every clear day, every 15 min (Holben et al. 1998). The
data accuracy is 0.01 (visible solar radiation) or 0.02 (ultraviolet) (Smirnov et al.
2000). The AERONET provides tree levels of data: level 1.0 (raw data), level 1.5
(cloud-screened data) and level 2.0 (quality-assured data). For the detailed
description see AERONET website (http://aeronet.gsfc.nasa.gov/).
The IOPAN based data obtained with a Microtops II sun photometer were
collected and processed with the pre- and post-field calibration, automatic cloud
clearing and were manually inspected. These portable instruments made by Solar
Light Company are capable of measuring the total ozone column, total precipitable
water vapor and aerosol optical depth (Morys et al. 2001; Ichoku et al. 2002). Each
of these parameters is automatically derived by the instrument from equations
installed by the manufacturer. The Microtops II instruments currently in use at the
IOPAN have five channels, but they may have one of two configurations: 340, 440,
675, 870, 936 nm or 440, 500, 675, 870, and 936 nm. The estimates of uncertainty
of the AOD in each channel oscillates around 0.02. Detailed instrument description
is available at the AERONET webpage (http://aeronet.gsfc.nasa.gov) and has been
presented by Markowicz et al. (2012) and Zawadzka et al. (2014).
In this paper, we also used the data from Koldeway Station in Ny-Alesund
performed by AWIPEV. Data from 2000 until 2012 were obtained using a fullautomatic sun photometer type SP1A produced by Dr. Schulz and Partner GmBH.
The instrument covers a spectral range from 350 to 1,050 nm in 17 channels. It
automatically tracks the sun, which ensures continuity of the measurements. The
AOD uncertainty is 0.01 (Toledano et al. 2012).
3 Methodology
The AOD is a key parameter in aerosol studies which describes the entire atmospheric column and is derived from the Beer-Bouger-Lambert law. In case of Cimel
and SP1A sun photometers the AOD is obtained using the following algorithm.
Annual Changes of Aerosol Optical Depth and Ångström Exponent …
27