MERIS albedo climatology for FRESCO+ O<sub>2</sub> A-band cloud retrieval
1
Citation
30
Reference
10
Related Paper
Abstract:
Abstract. A new global albedo climatology for Oxygen A-band cloud retrievals is presented. The climatology is based on MEdium Resolution Imaging Spectrometer (MERIS) Albedomap data and its favourable impact on the derivation of cloud fraction is demonstrated for the FRESCO+ (Fast Retrieval Scheme for Clouds from the Oxygen A-band) algorithm. To date, a relatively coarse resolution (1° × 1°) surface reflectance dataset from GOME (Global Ozone Monitoring Experiment) Lambert-equivalent reflectivity (LER) is used in FRESCO+. The GOME LER climatology does not account for the usually higher spatial resolution of UV/VIS instruments designed for trace gas remote sensing which introduces several artefacts, e.g. in regions with sharp spectral contrasts like coastlines or over bright surface targets. Therefore, MERIS black-sky albedo (BSA) data from the period October 2002 to October 2006 were aggregated to a grid of 0.25° × 0.25° for each month of the year and for different spectral channels. In contrary to other available surface reflectivity datasets, MERIS includes channels at 754 nm and 775 nm which are located close to the spectral windows required for O2 A-band cloud retrievals. The MERIS BSA in the near infrared compares well to Moderate Resolution Imaging Spectroradiometer (MODIS) derived BSA with an average difference lower than 1% and a correlation coefficient of 0.98. However, when relating MERIS BSA to GOME LER a distinctly lower correlation (0.80) and enhanced scatter is found. Effective cloud fractions from two exemplary months (January and July 2006) of Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) data were subsequently derived with FRESCO+ and compared to those from the Heidelberg Iterative Cloud Retrieval Utilities (HICRU) algorithm. The MERIS climatology generally improves FRESCO+ effective cloud fractions. In particular small cloud fractions are in better agreement with HICRU. This is of importance for atmospheric trace gas retrieval which relies on accurate cloud information at small cloud fractions. In addition, overestimates along coastlines and underestimates in the Intertropical Convergence Zone introduced by the GOME LER were eliminated. While effective cloud fractions over the Saharan desert and the Arabian peninsula are successfully reduced in January, they are still too high in July relative to HICRU due to FRESCO+'s large sensitivity to albedo inaccuracies of highly reflecting targets and inappropriate aerosol information which hampers an accurate albedo retrieval. Apart from FRESCO+, the new MERIS albedo data base is applicable to any cloud retrieval algorithms using the O2 A-band or the O2-O2 absorption band around 477 nm. Moreover, the by-product of BSA at 442 nm can be used in NO2 remote sensing and the BSA at 620 nm, 665 nm, and 681 nm could be integrated in current H2O retrievals.Keywords:
Imaging spectrometer
Albedo (alchemy)
Moderate-resolution imaging spectroradiometer
Cloud fraction
Satellite remote sensing has been used extensively for many years to monitor the open oceans and coastal waters. These methods have been extended more recently to the study of inland waters. In this study we consider the potential application of data from two ocean color sensors, Moderate‐Resolution Imaging Spectroradiometer (MODIS) and Medium‐Resolution Imaging Spectrometer (MERIS), for monitoring the levels of suspended solids in small and intermediate sized lakes and reservoirs. We measured total suspended matter (TSM) in four southwestern United States lakes, Roosevelt Lake, Saguaro Lake, Bartlett Lake, and Lake Pleasant, and compared these field data with images obtained from these medium resolution satellite sensors. Our regression analysis of the complete data set identified a linear relationship between the field TSM values and both MODIS 250 m data ( r 2 = 0.461) and MERIS 290 m data ( r 2 = 0.521). This relationship improved substantially when data from the smallest lake in the study (Saguaro Lake) were excluded from the analysis ( r 2 = 0.819 and r 2 = 0.888, respectively). The resultant linear models produced estimates with a root‐mean‐square error (RMSE) ranging from 3.14 mg/L (MODIS) and 2.04 mg/L (MERIS) for all four lakes combined, improving to 1.32 mg/L (MODIS) and 0.47 mg/L (MERIS) for a lake‐specific regression. These results suggest that these satellite sensors have the potential to effectively monitor TSM in lakes and reservoirs, although a minimum practical lake size does appear to exist.
Moderate-resolution imaging spectroradiometer
Imaging spectrometer
Spectroradiometer
Cite
Citations (47)
In this study we use the capabilities of the MODerate Resolution Imaging Spectroradiometer (MODIS) land surface product to estimate the radiative forcing due to surface albedo changes caused by anthropogenic vegetation changes. We improve the representation of the present surface albedo by using data retrieved from MODIS. The change in surface albedo is based on the current vegetation land cover from MODIS, the MODIS surface albedos for those vegetation types, and a data set for potential natural vegetation. We arrive at a radiative forcing due to anthropogenic vegetation changes of −0.09 Wm −2 since pre‐agriculture times to present, weaker than most earlier published results for this climate forcing mechanism. This is mainly due to a lower surface albedo associated with cropland and further with the use of MODIS data to allow us to constrain the surface albedo change.
Albedo (alchemy)
Moderate-resolution imaging spectroradiometer
Forcing (mathematics)
Cite
Citations (89)
Cloud masks are the final product of cloud detection and the starting point for determining the cloud amount. To calculate the cloud amount within thematic classes of cloud masks, the cloud fraction for each class must be assigned. This is usually done subjectively, assuming that clear pixels indicate a cloud fraction value of 0.0 and cloudy pixels indicate a cloud fraction value of 1.0. An analogous interpretation can also be applied using the Moderate Resolution Imaging Spectroradiometer (MODIS) level 3 approach (L3), which calculates global cloud amounts from instantaneous cloud masks. In this paper, the cloud fractions for each of the four MODIS cloud mask classes were derived in a more objective manner. They were based on high‐resolution Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) observations that were collocated in space and time with MODIS data. This study was limited to cumulus and stratocumulus clouds observed during the daytime over the ocean surface with a MODIS nadir viewing geometry. Cloud fraction values were averaged and used to calculate the cloud amounts for all analyzed ASTER scenes, which were then compared to statistics that assumed an L3 approach. Our results show that the L3 approach tended to overestimate the cloud amount in general by 0.087, and this value ranged between 0.007 and 0.100, depending on the observation conditions. We found that cloud fraction values were influenced by the average cloud amount in the analyzed ASTER scenes, especially in the case of “cloudy” and “uncertain” pixels. The MODIS 250 m cloud mask was also evaluated and found to be a reasonable source of cloud fraction information for cloud mask classes during the daytime over the ocean, reducing L3 overestimation by approximately 30%.
Cloud fraction
Moderate-resolution imaging spectroradiometer
Cloud top
Spectroradiometer
Cloud height
Advanced very-high-resolution radiometer
Effective radius
Cite
Citations (18)
Using 15‐year observations obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board both NASA Terra and Aqua from March 2003 to February 2018, this study investigated the spatio‐temporal variations of both macro‐ and micro‐physical cloud properties over China, including cloud fraction (CF), cloud top pressure (CTP), cloud top temperature (CTT), cloud optical thickness (COT), and effective radius ( r e ) of both liquid water and ice clouds. Multi‐year averaged CF is around 61% over whole China region. However, CF varies with both regions and seasons. The CFs are about 6–8% larger in summer and winter (~64–65%) than in spring and autumn (~58%). By classifying China into five regimes, which are northwestern China (NW), northeastern China (NE), Tibetan Plateau (TP), northern China (N), and southern China (S), there is a clear CF regional distribution pattern. In general, there are large amount of clouds in S and southeast of TP, and small amount in NE, N, NW and most TP. Moreover, there are generally more clouds over ocean than over land, and much more clouds over S than over N. The CFs are larger (smaller) in the afternoon than in the morning over most land (ocean) regions. Furthermore, the largest CF differences between afternoon and morning occur over the TP region in China. COT demonstrates almost the same regional distribution pattern as the CF for all four seasons. Specifically, COT is higher in S than in N, which is most likely associated with the type of clouds and the availability of water vapour. Cloud r e shows larger values in NW and TP than in eastern China regions in all seasons except for summer, which could be related to the heavy aerosol pollution in eastern China regions. Accompanying with the cold cloud tops over TP, a low CTP centre is often located there.
Moderate-resolution imaging spectroradiometer
Cloud fraction
Effective radius
Cloud top
Cite
Citations (86)
ABSTRACT Surface‐based and satellite‐based observations remain the fundamental source of cloud amount data for climatologists. However, both data sets show inconsistency related to the interpretation of instantaneous cloud detection, whether measured using the okta scale for surface‐based ( SYNOP ) observations or cloud mask classes (for satellite‐based observations). This study compared mean monthly SYNOP cloud amount with those reported for the moderate resolution imaging spectroradiometer ( MODIS ) cloud imager onboard Aqua and Terra satellites. Data were collected simultaneously (±10 min) over Poland between 2003 and 2013 (a total of 3240 MODIS passes). Results showed that in daytime conditions the average range of inconsistency for SYNOP (10.8%) is similar to MODIS (10.1%). However, for MODIS it doubles (20.9%) at nighttime. This is attributed to the change in frequency of MODIS cloud mask intermediate classes. Furthermore, in particular months' range of inconsistency for MODIS exceeded 20% in daytime and 50% at nighttime, while maximum values for SYNOP were always lower than 20% (a consequence of the okta scale). The findings also confirmed that the standard procedure used to interpret SYNOP okta values (i.e. the assumption that 1 okta equals 12.5%) is a relatively accurate (±2%) estimate of monthly mean cloud amount, although this assumes that surface‐based observers always correctly assign the correct okta value to the cloud fraction. Finally, the error in the SYNOP cloud amount estimation was correlated with the average cloud amount for a given location. Those findings will improve the reliability of cloud amount validation efforts that use SYNOP data as a reference.
Moderate-resolution imaging spectroradiometer
Cloud fraction
Cloud top
Cloud height
Cite
Citations (10)
An evaluation of the Moderate‐Resolution Imaging Spectroradiometer (MODIS) global land surface albedo product is essential for its use in scientific studies. We evaluate the accuracy of the albedo product with nearly 3 years (from January 2001 to July 2003) of ground measurements from the Gaize Automatic Weather Station (32.30°N, 84.06°E, 4420 m) on the western Tibetan Plateau. The land surface consists of semidesert or desert soil. Vegetation in this region is very rare. A comparison with field measurements shows that the MODIS global land surface albedo meets an absolute accuracy requirement of 0.02. There is no distinctive bias between the MODIS‐derived albedo and the ground‐measured albedo, with a root‐mean‐square error of 0.0186 and a maximum error of 0.036.
Albedo (alchemy)
Moderate-resolution imaging spectroradiometer
Spectroradiometer
Cite
Citations (103)
Abstract Over the ablation period of 2004, daily snow albedo values retrieved from the moderate‐resolution imaging spectroradiometer (MODIS) Terra were compared with ground‐based albedo measurements. Two data sets are used for this study. The first data set is from two automatic weather stations (AWS) located at fixed points in Karasu basin in eastern Turkey. This provided the temporal assessment of MODIS daily snow albedo values. The second data set, consisting of 19 observation points randomly distributed around one of the AWS sites, enables the spatial variability assessment of MODIS albedo retrievals. Both MODIS and in situ albedo observations were aggregated in a geographic information system for further analysis. Generally, MODIS albedo values were within 10% of the in situ values. Reductions in albedo values were observed both in MODIS and field observations as snow depth decreased and snow water equivalent increased. Copyright © 2006 John Wiley & Sons, Ltd.
Albedo (alchemy)
Moderate-resolution imaging spectroradiometer
Spectroradiometer
Data set
Cite
Citations (40)
Clouds can influence climate through many complex interactions within the hydrological cycle. Due to the important effects of cloud cover on climate, it is essential to study its variability over certain geographical areas. This study provides a spatial and temporal distribution of sky conditions, cloudy, partly cloudy, and clear days, in Iran. Cloud fraction parameters were calculated based on the cloud product (collection 6_L2) obtained from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on board the Terra (MOD06) and Aqua (MYD06) satellites. The cloud products were collected daily from January 1, 2003 to December 31, 2014 (12 years) with a spatial resolution of 5 km × 5 km. First, the cloud fraction data were converted into a regular geographic coordinate network over Iran. Then, the estimations from both sensors were analyzed. Results revealed that the maximum annual frequency of cloudy days occurs along the southern shores of the Caspian Sea, while the minimum annual frequency occurs in southeast Iran. On average, the annual number of cloudy and clear-sky days was 88 and 256 d from MODIS Terra, as compared to 96 and 244 d from MODIS Aqua. Generally, cloudy and partly cloudy days decrease from north to south, and MODIS Aqua overestimates the cloudy and partly cloudy days compared to MODIS Terra.
Moderate-resolution imaging spectroradiometer
Cloud fraction
Annual cycle
Cloud top
Spectroradiometer
Cite
Citations (1)
Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging SpectroRadiometer (MISR) are widely used remote sensors. Their albedo products over snow are compared with in situ data from the Greenland Climate Network (GC-Net). MODIS can catch the long term albedo change over Greenland. Considering several uncertainties in origin, MODIS and MISR albedo products agree with in situ albedo within the limits of accuracy and temporal representativeness.
Moderate-resolution imaging spectroradiometer
Albedo (alchemy)
Spectroradiometer
Cite
Citations (2)