ALBERT

Description: Data of the broadband albedo averaged at the MODIS pixel, which was derived from the measurements by either pyrometer (shortwave, in the range of 200-3600 nm) or albedometer (visible in 400-700nm, near infrared in 700-2100, and shortwave in 400-2100) during the ACLOUD and AFLUX campaigns. This data is intended to validate the RTM-SciML (short for radiative transfer model - scientific machine learning model) algorithm, which uses top-of-atmosphere radiance data from MODIS as input to perform albedo retrieval for sea-ice surface. In addition to the satellite and measured data, the pixel type and surface classification retrieved using scientific machine learning models (https://tc.copernicus.org/preprints/tc-2021-397/) are also included.

Description: Data of the broadband albedo averaged at the MODIS pixel, which was derived from the measurements by either pyrometer (shortwave, in the range of 200-3600 nm) or albedometer (visible in 400-700nm, near infrared in 700-2100, and shortwave in 400-2100) during the ACLOUD and AFLUX campaigns. This data is intended to validate the RTM-SciML (short for radiative transfer model - scientific machine learning model) algorithm, which uses top-of-atmosphere radiance data from MODIS as input to perform albedo retrieval for sea-ice surface. In addition to the satellite and measured data, the pixel type and surface classification retrieved using scientific machine learning models (https://tc.copernicus.org/preprints/tc-2021-397/) are also included.

Description: Questions: How do population structure and recruitment characteristics of Betula saplings beyond the treeline vary among climatic regions, and what is the potential for development into tree-sized individuals with interacting grazing pressure? Location: Scandes Mountains. Methods: Sapling characteristics of Betula pubescens subsp. tortuosa, their topographic position above the treeline, growth habitat and evidence of recent grazing was investigated in three areas with a long continuous grazing history, along a latitudinal gradient (62-69°N). Results: Saplings were common up to 100 m above the treeline in all areas. The northern areas were characterised by small (〈30 cm) and young (mean 14 years old) saplings in exposed micro-topographic locations unfavourable to long-term survival. In the southern area, broad height (2-183 cm) and age (4-95 years; mean 32 years) distributions were found in sheltered locations. Age declined with altitude in all areas. Sapling growth rate varied within and between areas, and the age x height interaction was significant only in the southern area. Growth rates decreased from south to north and indicated a considerable time required to reach tree size under prevailing conditions. Conclusions: Regional differences can be attributed to climatic differences, however, interacting biotic and abiotic factors such as micro-topography, climate and herbivory, mutually affect the characteristics of birch saplings. In view of the long time needed to reach tree size, the generally expected evident and fast treeline advance in response to climate warming may not be a likely short-term scenario. The sapling pool in the southern region possesses strongest potential for treeline advance.

Description: We have examined several approaches for estimating the surface concentration of particulate organic carbon, POC, from optical measurements of spectral remote-sensing reflectance, Rrs(Lambda), using field data collected in tropical and subtropical waters of the eastern South Pacific and eastern Atlantic Oceans. These approaches include a direct empirical relationship between POC and the blue-to-green band ratio of reflectance, Rrs(Lambda B)/Rrs(555), and two-step algorithms that consist of relationships linking reflectance to an inherent optical property IOP (beam attenuation or backscattering coefficient) and POC to the IOP. We considered two-step empirical algorithms that exclusively include pairs of empirical relationships and two-step hybrid algorithms that consist of semianalytical models and empirical relationships. The surface POC in our data set ranges from about 10 mg/m**3 within the South Pacific Subtropical Gyre to 270 mg/m**3 in the Chilean upwelling area, and ancillary data suggest a considerable variation in the characteristics of particulate assemblages in the investigated waters. The POC algorithm based on the direct relationship between POC and Rrs(Lambda B)/Rrs(555) promises reasonably good performance in the vast areas of the open ocean covering different provinces from hyperoligotrophic and oligotrophic waters within subtropical gyres to eutrophic coastal upwelling regimes characteristic of eastern ocean boundaries. The best error statistics were found for power function fits to the data of POC vs. Rrs(443)/Rrs(555) and POC vs. Rrs(490)/Rrs(555). For our data set that includes over 50 data pairs, these relationships are characterized by the mean normalized bias of about 2% and the normalized root mean square error of about 20%. We recommend that these algorithms be implemented for routine processing of ocean color satellite data to produce maps of surface POC with the status of an evaluation data product for continued work on algorithm development and refinements. The two-step algorithms also deserve further attention because they can utilize various models for estimating IOPs from reflectance, offer advantages for developing an understanding of bio-optical variability underlying the algorithms, and provide flexibility for regional or seasonal parameterizations of the algorithms.

Description: The CoastColour project Round Robin (CCRR) project (http://www.coastcolour.org) funded by the European Space Agency (ESA) was designed to bring together a variety of reference datasets and to use these to test algorithms and assess their accuracy for retrieving water quality parameters. This information was then developed to help end-users of remote sensing products to select the most accurate algorithms for their coastal region. To facilitate this, an inter-comparison of the performance of algorithms for the retrieval of in-water properties over coastal waters was carried out. The comparison used three types of datasets on which ocean colour algorithms were tested. The description and comparison of the three datasets are the focus of this paper, and include the Medium Resolution Imaging Spectrometer (MERIS) Level 2 match-ups, in situ reflectance measurements and data generated by a radiative transfer model (HydroLight). The datasets mainly consisted of 6,484 marine reflectance associated with various geometrical (sensor viewing and solar angles) and sky conditions and water constituents: Total Suspended Matter (TSM) and Chlorophyll-a (CHL) concentrations, and the absorption of Coloured Dissolved Organic Matter (CDOM). Inherent optical properties were also provided in the simulated datasets (5,000 simulations) and from 3,054 match-up locations. The distributions of reflectance at selected MERIS bands and band ratios, CHL and TSM as a function of reflectance, from the three datasets are compared. Match-up and in situ sites where deviations occur are identified. The distribution of the three reflectance datasets are also compared to the simulated and in situ reflectances used previously by the International Ocean Colour Coordinating Group (IOCCG, 2006) for algorithm testing, showing a clear extension of the CCRR data which covers more turbid waters.

Description: The relationship between phytoplankton assemblages and the associated optical properties of the water body is important for the further development of algorithms for large-scale remote sensing of phytoplankton biomass and the identification of phytoplankton functional types (PFTs), which are often representative for different biogeochemical export scenarios. Optical in-situ measurements aid in the identification of phytoplankton groups with differing pigment compositions and are widely used to validate remote sensing data. In this study we present results from an interdisciplinary cruise aboard the RV Polarstern along a north-to-south transect in the eastern Atlantic Ocean in November 2008. Phytoplankton community composition was identified using a broad set of in-situ measurements. Water samples from the surface and the depth of maximum chlorophyll concentration were analyzed by high performance liquid chromatography (HPLC), flow cytometry, spectrophotometry and microscopy. Simultaneously, the above- and underwater light field was measured by a set of high spectral resolution (hyperspectral) radiometers. An unsupervised cluster algorithm applied to the measured parameters allowed us to define bio-optical provinces, which we compared to ecological provinces proposed elsewhere in the literature. As could be expected, picophytoplankton was responsible for most of the variability of PFTs in the eastern Atlantic Ocean. Our bio-optical clusters agreed well with established provinces and thus can be used to classify areas of similar biogeography. This method has the potential to become an automated approach where satellite data could be used to identify shifting boundaries of established ecological provinces or to track exceptions from the rule to improve our understanding of the biogeochemical cycles in the ocean.

Description: Atlantic herring, Clupea harengus, have complex population structures and different populations can be found in fully marine, as well as nearly freshwater conditions. Mixing of populations is known, but the extent of connectivity is still unclear. Ripe spring spawning herring were collected in marine (salinity 35, Atlantic) and brackish water (salinity 6, Baltic Sea) conditions. One Atlantic herring female was crossed with one Atlantic and one Baltic male generating an F1-generation consisting of Atlantic purebreds and Atlantic/Baltic hybrids which were incubated and co-reared at two different salinities, 16 and 35 respectively, for three years. The F1-generation was repeatedly sampled for length measurements, vertebral counts and otoliths were also extracted for shape analysis. Atlantic purebreds grew better than Atlantic/Baltic hybrids at salinity 35, but not at salinity 16. In contrast, Atlantic/Baltic hybrids achieved larger size-at-age than the wild caught Baltic parental group. Mean vertebral counts and otolith aspect ratios were higher for Atlantic purebreds than Atlantic/Baltic hybrids, consistent with the parental groups. There were no differences in vertebral counts and otolith aspect ratios between herring with the same genotype but raised in different salinities. A Canonical Analysis of Principal Coordinates was applied to analyze the variation in wavelet coefficients that described otolith shape. The first discriminating axis identified the differences between Atlantic purebreds and Atlantic/Baltic hybrids, while the second axis represented salinity differences. These results demonstrate that otolith shape and vertebral counts have a significant genetic component and are therefore useful for studies on population dynamics and connectivity.

Description: We present a data set on particulate absorption line height at 676 and surface Chl-a concentration using underway spectrophotometry (Wetlabs AC-s instrument) and collocated discrete water sampling (measured by High Pressure Liquid Chromatography, HPLC, and Quantitative Filtration Technique) during two summer cruises PS93.2 and PS99.2 in the Fram Strait. Additionally we present for the discrete water samples the fraction of different phytoplankton groups on the total biomass, approximated by the chl-a concentration, which are derived from phytoplankton marker pigments also measured by HPLC.

Description: Lake Arendsee originated from salt depressions (sinkhole) 822 A.D. and in 1685 (Scharf 1998). Due to the maximum depth of 49 m (mean depth 29 m) and a surface area of about 5 km², Lake Arendsee has a volume of approx. 150 Mio. m³. According to Scharf (1998), eutrophication dates back to 1970 when sewage loading of the town of Arendsee and drainage of Lake Fauler See into Lake Arendsee raised nutrient loading. Due to the long residence time of 114 years, no recovery of the lake occurred up to now although several restoration measures were applied (e.g. Stüben et al. 1998; Hupfer and Lewandowski 2005). Lake Arendsee regularly expresses, large, surface scum forming blooms of cyanobacteria. This publication series includes datasets collected on Lake Arendsee during the Inland Water Remote Sensing Validation Campaign 2017 (Bumberger et al. 2023).