Investigations into the development of a satellite-based aerosol climate data record using ATSR-2, AATSR and AVHRR data over north-eastern China from 1987 to 2012
Authors: Che Yahui , Guang Jie , de Leeuw Gerrit , Xue Yong , Sun Ling , Che Huizheng 
Published: July 2019

Abstract. Satellites provide information on the temporal and spatial
distributions of aerosols on regional and global scales. With the same
method applied to a single sensor all over the world, a consistent data set
is to be expected. However, the application of different retrieval
algorithms to the same sensor and the use of a series of different sensors
may lead to substantial differences, and no single sensor or algorithm is
better than any other everywhere and at all times. For the production of
long-term climate data records, the use of multiple sensors cannot be
avoided. The Along Track Scanning Radiometer (ATSR-2) and the Advanced ATSR
(AATSR) aerosol optical depth (AOD) data sets have been used to provide a
global AOD data record over land and ocean of 17 years (1995–2012), which is
planned to be extended with AOD retrieved from a similar sensor. To
investigate the possibility of extending the ATSR data record to earlier years,
the use of an AOD data set from the Advanced Very High Resolution Radiometer
(AVHRR) is investigated. AOD data sets used in this study were retrieved
from the ATSR sensors using the ATSR Dual View algorithm ADV version 2.31, developed
by Finnish Meteorological Institute (FMI), and from the AVHRR sensors using
the aerosol optical depth over land (ADL) algorithm developed by RADI/CAS. Together, these data sets cover a
multi-decadal period (1987–2012). The study area includes two contrasting
areas, both in regards to aerosol content and composition and surface
properties, i.e. a region over north-eastern China, encompassing a highly
populated urban/industrialized area (Beijing–Tianjin–Hebei) and a sparsely
populated mountainous area. Ground-based AOD observations available from ground-based sun photometer AOD
data in AERONET and CARSNET are used as a reference, together with broadband
extinction method (BEM) data at Beijing to cover the time before sun
photometer observations became available in the early 2000s. In addition,
MODIS-Terra C6.1 AOD data are used as a reference data set over the wide area
where no ground-based data are available. All satellite data over the study
area were validated against the reference data, showing the qualification of
MODIS for comparison with ATSR and AVHRR. The comparison with MODIS shows
that AVHRR performs better than ATSR in the north of the study area
(40∘ N), whereas further south ATSR provides better results. The
validation against sun photometer AOD shows that both AVHRR and ATSR
underestimate the AOD, with ATSR failing to provide reliable results in the
wintertime. This is likely due to the highly reflecting surface in the dry
season, when AVHRR-retrieved AOD traces both MODIS and reference AOD data
well. However, AVHRR does not provide AOD larger than about 0.6 and hence is
not reliable when high AOD values have been observed over the last decade.
In these cases, ATSR performs much better for AOD up to about 1.3.
AVHRR-retrieved AOD compares favourably with BEM AOD, except
for AOD higher than about 0.6. These comparisons lead to the conclusion that
AVHRR and ATSR AOD data records each have their strengths and weaknesses
that need to be accounted for when combining them in a single multi-decadal
climate data record.