Satellite Oceanography

The ETSI DVB-S2 telecom standard (EN 302307) was initially approved in 2005 to increase power and bandwidth efficiencies for telecom applications. This DVB-S2 standard has now replaced the historical DVB-S standard for most of satellite television broadcasting applications. An upgrade of the standard, called DVB-S2X, has been approved in 2014, and its deployment is on-going.

In parallel, in the satellite Earth observation community, the DVB-S2 standard has naturally appeared as a good candidate for new telemetry applications, and in particular for High Data Rate Telemetry (HDRT) applications in EESS X-band (8.025-8.4 GHz) or EESS Ka-band (25.5-27 GHz).

A CCSDS adaptation profile of the DVB-S2 standard has been approved as a CCSDS Recommended Standard (131.3) in 2013. The DVB-S2 standard is used for X-band HDRT of Flock satellites (by Planet Labs).

The DVB-S2 standard was chosen for many HDRT preliminary developments and is expected to be used on many (other) operational systems soon.

The aim of this paper is to present the DVB-S2 standard, its capabilities and its current and future applications in HDRT. The outline of the paper is the following: a first section presents the DVB-S2 standard (the version endorsed by CCSDS, the upgraded version DVB-S2X and ETSI and CCSDS guidelines). A second section recalls the VCM
(Variable Coding and Modulation) and ACM (Adaptive Coding and Modulation) capabilities of DVB-S2, some implementation issues about VCM and ACM and some system analysis results (link budget, downloading capacity). A third part proposes to look over equipments and programs already using DVB-S2 or expecting to use DVB-S2 in a close future.

The sea surface temperature (SST) is an important factor and indicator of the sea water
quality, with various ecological and anthropogenic implications. We used high-resolution satellitederived
SST data, in tandem with field observations and long-term meteorological data, to investigate
the spatial and interannual SST variability over the Aegean, Ionian, and Cretan (AIC) Seas during the
recent 14-year period (2008–2021). Increasing trends were identified for most of the sub-basins of the
AIC Seas. The numbers and durations (days) of the marine heat waves (MHWs) have significantly
increased, especially during the last quadrennial period (2018–2021). Changes have been detected in
both the maximum and minimum values; however, the trend of the mean annual values is mainly
associated with the interannual increases in the lowest values (weaker minima during the cold
seasons). The interannual variability and the increasing positive trends of the air temperature are
very similar to the SST variations, showing a 5-to-10-day lag between the seasonal time series of
the two parameters for all regions; however, extreme atmospheric events (e.g., cold fronts or heat
waves) have a more direct impact on the SST variability (zero lag). MHWs were more frequent over
the northern Aegean Sea, especially in Thermaikos Gulf, which is characterized as a “hot spot” for
MHWs. MHWs were rarer over the southern regions, especially over the southeastern Aegean and
Cretan Seas. A stratified upper ocean, controlled by buoyant brackish plumes, such as the Black Sea
Waters (BSW) in the northern Aegean, may increase the heat storage capacity of the surface water
masses, contributing to the further warming of the ocean. This was the case in the summer of 2021,
which was a unique year for the AIC Seas, and especially for the northern Aegean, which revealed
the highest SST values among all the study years. The satellite-derived observations of the 2008–2021
period showed increasing trends for all coastal waters, strong trend slopes for most of the coasts of
the northern Aegean and central Ionian Seas, and milder trend slopes in the eastern Aegean.

Analysis of relationship between sea surface temperature (SST) and chlorophyll-a (chl-a) increases our
understanding on the productivity of the ocean. Satellite images provide reliable important information on oceanographic
conditions and simultaneously support marine environmental monitoring and assessment. Monthly images of Moderate
Resolution Imaging Spectroradiometer satellite (MODIS-Aqua) derived chl-a and SST from July 2002 to June 2011
around archipelagic waters of Spermonde Indonesia were used to investigate the relationship between SST and chl-a.
While the daily data were used to produce the potential fishing ground maps of Rastrelliger kanagurta at the study area.
Climatological images showed that the SST during the Southeast monsoon is lower thanthe Northwest monsoon, while
chl-a during the Southeast monsoon is higher than the Northwest monsoonand isscattered along the coast. SST and chl-a
showed an inverse correlation, with coefficient of correlation at R = 0.542. Preferred range of R. kanagurta were 30.75 ±
0.21oC for SST and 0.31 ± 0.10 mg m-3 for chl-a. Potential fishing grounds were found located around the coast. This
study indicates that satellite image is able to determine the relationship between SST and chl-a and identify aggregation
grounds of R. kanagurta.

Current dynamics in the Strait of Bonifacio (south Corsica) were investigated at a small scale during the STELLAMARE1 multidisciplinary cruise in summer 2012, using in situ measurements and modeling data. The Strait of Bonifacio is a particularly sensitive marine area in which specific conservation measures have been taken to preserve the natural environment and wild species. Good knowledge of the hydrodynamics in this area is essential to optimize the Marine Protected Area’s management rules. Therefore, we used a high-resolution model (400 m) based on the MARS3D code to investigate the main flux exchanges and to formulate certain hypotheses about the formation of possible eddy structures.
The aim of the present paper is first to synthetize the results obtained by combining Acoustic Doppler Current Profiler data, hydrological parameters, Lagrangian drifter data, and satellite observations such as MODIS OC5 chlorophyll a data or Metop-A AVHRR Sea Surface Temperature (SST) data. These elements are then used to validate the presence of the mesoscale eddies simulated by the model and their  recurrence outside the cruise period. To complete the analysis, the response of the 3D hydrodynamical model was evaluated under two opposing wind systems and certain biases were detected.
Strong velocities up to 1 m s−1 were recorded in the east part due to the Venturi effect; a complementary system of vortices governed by Coriolis effect and west wind was  observed in the west part, and horizontal stratification in the
central part has been identified under typical wind condition.

An experimental deployment of a new type of unmanned vessel is presented. The Christian Michelsen Research SailBuoy, a remotely-controlled surface vehicle, sampled near-surface properties during a two-month mission in the northern Gulf of Mexico in March – May, 2013. Averaged over the entire deployment, the vessel speed over ground was 42 ± 30 cm s-1 (± one standard deviation) with a maximum of 180 cm s-1. During the 62 days of the mission, the SailBuoy covered a total range of approximately 400 km in both meridional and zonal directions, with a cumulative total distance of approximately 2400 km. Three parameters were recorded: sea surface temperature, conductivity, and dissolved oxygen. Observed surface temperature and salinity records are compared with remote sensing data and the salinity fields from a regional ocean modeling system, respectively. The absolute error compared to remote sensing data to surface temperature is on average approximately 0.5°C. The comparison with the full Gulf of Mexico and the nested Northern Gulf of Mexico HYCOM models demonstrates the validity and usefulness of SailBuoy measurements and the instrument’s utility in evaluating fields produced by ocean models having different attributes. The potential of the SailBuoy for mapping a large-scale river plume, which would be challenging or costly with conventional ship surveys and/or remote sensing, is demonstrated.

Some researchers have suggested that corals living in deeper reefs may escape heat stress experienced by shallow corals. We evaluated the potential of deep coral reef refugia from bleaching stress by leveraging a long record of satellite-derived sea surface temperature data with a temporal, spatial, and depth precision of in situ temperature records. We calculated an in situ stress metric using a depth bias-adjusted threshold for 457 coral reef sites among 49 islands in the western and central Pacific Ocean over the period 2001-2017. Analysis of 1,453 heating events found no meaningful depth refuge from heat stress down to 38 m, and no significant association between depth and subsurface heat stress. Further, the surface metric underestimated subsurface stress by an average of 39.3%, across all depths. combining satellite and in situ temperature data can provide bleaching-relevant heat stress results to avoid misrepresentation of heat stress exposure at shallow reefs. Mass coral bleaching events due to anomalously warm ocean water have increased in both frequency and severity, and represent a significant threat to coral reef ecosystems worldwide 1-4. Coral bleaching occurs when environmental stressors cause a breakdown in the relationship between corals and their algal endosymbionts 5. Mass coral bleaching is most commonly caused by abnormally high temperatures, 1-2 °C above the usual summer maximum for several weeks and can result in widespread coral mortality 5-8. Coral mortality, in turn, can reduce coral diversity and habitat complexity 8,9 and negatively impact species richness, abundance, and biomass of coral reef fishes and other associated biodiversity 8,10,11. These attendant ecological consequences of mass coral bleaching and the corresponding declines in ecosystem services (e.g., food source, fisheries, and tourism) support the need for an accurate understanding of heat stress exposure on corals. Currently, scientists and managers primarily use satellite-derived sea surface temperature (SST) data products to understand heat stress and predict coral bleaching due to the near real-time availability, global coverage, and ease of data access. The most extensively used metric is the Degree Heating Week 12 developed by the U.S. National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch (CRW) program 3. Despite the continued improvement and validation of SST data and satellite-derived products 6,13,14 , uncertainty has continued to exist in how well the SST data and derived metrics represent in situ conditions on coral reefs, especially at depth 15,16. Sources of uncertainty include: (1) depth-satellites measure the radiance from the ocean skin layer (upper ~10 μm) to derive temperature (that is typically cooler than the surface water below due to evaporative cooling) in contrast to loggers that measure at the depth of their deployment; (2) spatial scale-satellite measurements integrate across a large area (hundreds of square meters to square kilometers) compared with the point measurement of an in situ temperature logger; and (3) temporal scale-the frequency of satellite temperature measurements is typically once per 3-12 hours (but up to 6 times per hour in some regions), with data products derived from these reported once per day; in contrast, in situ measurements are typically logged once per 5-30 minutes. As infrared

Datos de captura y esfuerzo de la pesquería cerquera de atún aleta amarilla (Thunnus albacares) e imágenes satelitales mensuales de la temperatura superficial del mar (TSM) obtenidas del sensor Radiómetro Avanzado de Muy Alta Resolución (AVHRR) fueron usadas para examinar la relación entre la agregación de atún aleta amarilla y la distribución de TSM en el Pacífico tropical oriental durante el período 1995-2003. Valores mensuales de captura por unidad de esfuerzo (CPUE) fueron calculados como la captura en toneladas métricas/el número de días de pesca en una cuadrícula de 1º de latitud x 1º de longitud y utilizados como el índice relativo de abundancia. En total, 33.542 datos de CPUE de aleta amarilla fueron utilizados. Los resultados obtenidos permiten establecer el rango de TSM entre 26ºC y 30ºC como el rango térmico “preferido” del atún aleta amarilla en el Pacífico tropical oriental, y el rango de TSM entre 28ºC y 30ºC como el rango de temperatura más favorable para la pesca exitosa de aleta amarilla. La consistente ocurrencia de atún aleta amarilla en la relativamente delgada capa de mezcla superficial (≈40-50 m) de temperatura homogénea predominante en el Pacífico tropical oriental sugiere que el rango de TSM “preferido” del atún aleta amarilla encontrado en este estudio puede ser representativo del hábitat térmico óptimo de esta especie.

Thermaikos Gulf, located in the Northwestern Aegean Sea, is a marine ecosystem of major importance, not only environmentally, but also due to the various socioeconomic activities associated with area (Krestenitis et al., 2012). A multi-platform observational study was conducted in summer, autumn and winter 2017 to investigate the current quality state of seawater and seabed. Water and sediment samples were seasonally collected from three sampling stations located at the northern part of Thermaikos Gulf: two stations at the outfall areas of the Thessaloniki's Wastewater Treatment Plants (WTP) and one very close to the city's seafront. The measurements include the physical (CTD), chemical and biological characteristics of the water column (phytoplankton and protozooplankton community) and seabed (macro-invertebrates). Satellite data were also used to discuss the in situ findings. Very large temperature and chl-a differences were observed between Thessaloniki (inner) and Aggelohori (outer) Gulf in December. Very high surface concentrations of phosphates and total phosphorus were also measured, especially in Thessaloniki. The phytoplankton biomass was extremely high in the inner Gulf on July after the “dirty” Sea phenomenon and on December when strong Mesodinium rubrum red tide were observed in the inner Gulf. Polychaetes and mollusks prevailed in the sediment fauna. The density of macro-invertebrates was found very increased close to the seafront of Thessaloniki.Significant differences were detected in physical and biochemical characteristics between the inner and outer Gulf. More brackish waters were measured in summer than in fall and winter.

The concentration of water vapor in the marine atmospheric boundary layer (MABL) at the Brazil-Malvinas Confluence
(BMC), in the Southwestern Atlantic Ocean, was analyzed using data taken during ten oceanographic cruises conducted during the
months of October to November in 2004 to 2015. Previous works had shown that this region, known for its intense horizontal gradients
of sea surface temperature (SST), is responsible for the local modulation of CLAM and for the maintenance of intense lateral gradients
of latent and sensible heat flows between the atmosphere and the ocean. Our results show that the thermal gradients between the
warm waters of the Brazil Current (BC) and the cold waters of the Malvinas Current (MC) that meet at the BMC are able to produce
significant differences on the atmospheric water vapor content between both sides of the oceanographic front on the extension of the
MABL. On average over the warm waters of the BC, the MABL is more humid with an average value near 2 g.kg-1 higher than in
the cold region dominated by MC waters. The MABL is locally modulated by the SST as observed in other previous works made
for the same region. The atmospheric transient systems, common in this region of the planet, however, can attenuate or intensify the
concentration of water vapor in the MABL.

This work has evaluated the acoustic signal transmission loss in presence of the thermic gradient produced by the coastal upwelling of Cabo Frio – RJ. A hydrodynamic numerical model was used to built the thermohaline structure of the upwelling. This structure served as an input to an acoustic model and used like a base to the sound propagation. After this procedure, the acoustic signals were simulated in two different scenarios, one with the occurrence of a strong upwelling, and another with no upwelling. The result has shown that the upwelling plume acts as a barrier to the sound propagation. In the absence of upwelling, the acoustic signal could reach greater distances. Then, it's possible that the coastal upwelling can prevent the detection of submarine targets.