Spatial dispersion of aerial plankton over east-central Florida: Aeolian transport and coastline concentrations

Based on previous radar observations that diurnal 'aerial plankton' (i.e., the ensemble of small, weakly flying insects that drift with the wind ) is usually absent over the ocean, we hypothesized that the insect targets employ flight tactics to resist being drifted overwater. We expected that if aerial insects actively resist overwater drift, then (1) radar-observed clear-air echoes should accumulate along the coastline when winds blow offshore, but they should be advected inland rapidly when winds blow onshore; and (2) accumulations of aerial plankton should be greatest along stretches of coastline most nearly perpendicular to the ambient wind flow. We tested these predictions by comparing the distribution of clear-air radar reflectivity at different sites and under different regimes of wind during the Convection and Precipitation/Electrification (CaPE) Experiment, which was conducted on the east coast of Florida in the summer of 1991. Elevated levels of clearair reflectivity were evident along the coast on mornings when winds were from the west, but not on mornings with easterly winds. On days with westerly winds, this coastal enhancement occurred only in the morning, prior to the onset of the sea breeze. Following sea breeze development, coastal concentrations of clear-air echoes were advected westward and they dispersed rapidly; levels of clear-air reflectivity became depressed overall throughout the study area in the afternoon compared to the morning. Clear-air reflectivity was higher along a north-facing coastline compared to a south-facing coastline when winds had a northward component, with a mirror-image reversal of this pattern on days with southward winds. In contrast, clear-air echoes were uniformly nearly absent from the airspace over the adjacent ocean at all times of the day on all days. These findings support the hypothesis that the organisms comprising the aerial plankton respond behaviourally to coastlines to avoid being blown out to sea. Persistent concentrations of aerial plankton along coastlines may have important consequences for insect population dynamics and local ecosystem structure in coastal regions.     

Non-stationary and unequally spaced NDVI time series analyses by the LSWAVE software

ABSTRACT

Change detection within non-stationary and unequally spaced remote sensing time series has become a key methodology for a broad range of environmental applications. A new method of analysing vegetation variation over lands is proposed. Four regions in northern Tunisia with various characteristics are selected, and a non-stationary and unequally spaced Normalized Difference Vegetation Index (NDVI) time series is obtained for each region since 2000. The Landsat 7 remote sensing satellite imagery with insignificant cloud-shadow coverage is used to calculate the NDVI after atmospheric correction. The Least-Squares Wavelet (LSWAVE) software is implemented to rigorously analyse each NDVI time series and study the relationship between the vegetation of olive trees and temperature/precipitation in one of the regions. To investigate possible effects of temperature on the green cover caused by increasing water salinity, the coherency between the NDVI and sea surface temperature time series is also shown in the region of Lake Ichkeul in Tunisia.     

Surface currents off the west coast of Ireland studied from satellite images

Abstract

The surface current in the spring of 1984 off the west coast of Ireland has been mapped from NOAA-8 thermal infrared images. The “feature-tracking method” has been used to derive flow vectors from advective sea surface temperature feature displacements and elapsed time. This feature-tracking method has a great advantage which gives a synoptic and spatial view of the velocity distribution over in situ measurements. Sequential images obtained on orbits 5596, 5610 and 5627 during the period 25-27 April 1984 have been used and geometrically corrected. With the 24 hours and 48 hours differences, the measurement accuracy achieved in the speed of sea features was ±1 8cm/s. The surface current pattern agrees with the main current pattern obtained by ships and drift bottles. A cyclonic eddy centred at 57° 04′ N 10° 59′ W has been studied. A very pronounced feature recognized is the sea surface front between mixed coastal water and stratified Atlantic water along the whole west coast of Ireland. The front is characterized by cyclonic and anticyclonic eddies which have time scales of the order of 1 day to 7 days and length scales of the order of 30 km.     

The use of optic and radar satellite data for coastal environments

The pressure of population and its demands for fuel, for heating or industrial usage, causes destruction of the natural environment. One of the clearest examples for the accelerated degradation of changes in the forest area and coastline is in the Kilyos–Karaburun coastline located in the northern part of Istanbul metropolitan city. The open‐pit mining activities in the region are threatening the balances of both sea and land ecosystems, and cause degradation of forest areas and changes along the coastline. In this paper, the changes are examined with multisensor satellite data such as Landsat Thematic Mapper (TM), SPOT Panchromatic (P), and RADARSAT images by using different image‐processing techniques. The degrees of changes in coastline length and coastal region area were calculated, and the effectiveness of the use of different image data sets was outlined for coastal environments.     

Tropospheric ozone variability over the Indian coastline and adjacent land and sea

A tropospheric ozone variability study is carried out to investigate the spatial and temporal distribution over the coastline of the Indian peninsula and adjacent land and sea using NASA Langley Tropospheric Ozone Residual data set for the period 1979–2005. A strong seasonal cycle has been observed with large variation (～ 55%) over the upper eastern coast, followed by the upper and lower western coast, compared to the lower eastern coast (～ 33%). A negative gradient in ozone concentration is observed along eastern and western coasts during summer (slope ～ –0.78 and –0.65) and a positive gradient (slope ～ 0.16 and 0.21) during winter. The same is observed over the adjacent land and sea along the coastline with slight variation. This change in gradient can be attributed to the anthropogenic emission of precursor gases that reinforce localized photochemical production of ozone. In addition, topography, transport, seasonality of emission of precursor gases and the solar insolation cycle play a vital role.     

Shoreline changes in west-central Florida between 1987 and 2008 from Landsat observations

Shoreline changes caused by sediment erosion and accretion have important consequences for coastal ecosystems and coastal communities. Assessing such changes over long stretches of coastline, such as along the west-central Florida coast, represents a challenge to coastal zone managers. In this study, we used nine Landsat Thematic Mapper (TM) images from the west-central Florida coast (adjacent to Tampa Bay, FL) to study historical shoreline changes from 1987 to 2008. Specifically, we sought to evaluate the change of shorelines during the cold (1987–1998) and warm (1998–2008) phases of the Atlantic Multidecadal Oscillation (AMO). The cloud-free images selected for this study were collected during the periods when maximum tidal excursions were less than 9 cm from mean sea level, assuring minimal interference from tidal influence. The images revealed that the southern section of the Tampa Bay inlet showed a mean shoreline accretion rate of 1.30 m year^–1 and a cumulative mean shoreline change of 27.29 m over the past 21 years. The northern section of the Tampa Bay inlet showed a mean accretion rate of 0.34 m year^–1, with a cumulative mean shoreline change of 7.06 m during the past 21 years. Both sections experienced beach nourishment conducted by local communities which, while irregular, were effective in reducing beach erosion. The dynamics of opposing shores in the various inlets in the barrier islands of the study region varied substantially, with many showing accretion in the channel on one side but erosion on the other side.     

Remote-sensing monitoring for spatio-temporal dynamics of sand dredging activities at Poyang Lake in China

As the largest freshwater lake in China, Poyang Lake is suffering from declining water quality related to the excessive dredging of sand. Field supervision is difficult due to the size of the lake (>3000 km², wet season) and limited human resources. In this study, an approach is proposed to monitor sand-dredging activities using medium-resolution optical remote-sensing imagery, including 45 Landsat TM/ETM+ images from 2002 to 2012 and 140 HJ1A/B CCD images from 2009 to 2012. The procedure for detecting dredging vessels involves three steps. (1) The entire image is segmented into different homogeneous partitions to overcome water body heterogeneity, and ships in each partition with different levels of water clarity are detected using three types of contrast box architecture. (2) Dredging vessels are then identified based on a spatial overlay analysis of ships and dredging plumes, which are extracted from remote-sensing imagery. (3) False alarms (FAs) of dredging vessels are screened according to the distribution of the sandy lake bed. The results showed significant spatio-temporal variation in dredging activities; sand-dredging activities were concentrated at the northern part of Poyang Lake prior to 2008 and have expanded southwards since 2009. The northern part of the lake experienced persistent dredging operations throughout the year, whereas dredging was observed only during the wet seasons in the southern portion of the lake. A high intensity of illegal dredging was discovered based on two lines of evidence: dredging vessels were detected during the sand-dredging ban, and the estimated quantities of sand dredging were much higher than those planned by the authority. The sediment balance in Poyang Lake has continued to be disrupted, and the lake has become a sediment-exporting system. This study provides an effective solution for monitoring sand-dredging dynamics as well as useful information for managing sand dredging in fresh water environments and assessing its potential impacts on aquatic ecosystems.     

New products and projects

Abstract

This paper briefly describes the latest developments which have been made a CMS, Lannion, in the field of sea surface parameter restitution, i.e. the use of an interactive image processing system for sea surface temperature (SST) analysis over the Mediterranean Sea, the combined use of Meteosat and Advanced Very High Resolution Radiometer (AVHRR) data for SST field production, the routine production of surface solar irradiance fields and the survey of phytoplankton blooms with visible AVHRR data. This last experiment was made at the request of a group of French oceanographers.The other developmentsare parts of a programme aiming to retrieve small-scale characteristics of the ocean-atmosphere thermodynamics. The next main step of this programme is the extension of the use of an image processor to include an operational survey of the north-east Atlantic.     

Detecting and evaluating the influence of water depth,volume and altitude on the variations in the surface temperature of lakes using Landsat imagery

Abstract

The Landsat thermal band has been used to map the thermal pattern in three lakes of the English Lake District, Cumbria. The patterns arc clearly associated with the variations in the depth. The cause of the formation of this pattern is thought to be solar warming of water. The influence of water volume and altitude and the surface temperature and the relation among them were formalised in an equation involving 16 lakes.     

Landsat-satellite-based analysis of spatial–temporal dynamics and drivers of CyanoHABs in the plateau Lake Dianchi

ABSTRACT

Dianchi Lake, located in southwest China’s Yungui plateau, is facing severe eutrophication and frequent outbreaks of harmful cyanobacteria blooms (CyanoHABs). It is of great significance to monitor the occurrence and development of CyanoHABs in Dianchi Lake over a long period and analyse the main influences. Based on Landsat Thematic Mapper/Enhanced Thematic Mapper Plus/Operational Land Imager 1986–2016 data, we derived the distribution of the CyanoHABs in Dianchi Lake, and analysed spatial–temporal dynamics of the CyanoHABs by correlation with nutrition, meteorological, and humanities data. The results showed that the first outbreak of CyanoHABs in Dianchi Lake occurred in 1987, which is likely to be influenced by a rapid increase of nutrients in the lake, while the weather conditions also have some impact on the CyanoHABs occurrence. After 1990, the frequency of CyanoHABs is relatively high in the water near Longmen village, Fubao Bay, Hui Bay, and the lake inlet of the Panlong River to the north of Waihai in Dianchi Lake from June to November every year. Moreover, the CyanoHABs increased year by year until 2000. This is closely related to population growth and economic development. Furthermore, a large amount of precipitation and small wind speeds can also promote the occurrence of CyanoHABs. After 2000, the frequency of CyanoHABs decreased, as the large-scale management of water pollution in Dianchi Lake achieved certain effects. The area and frequency of CyanoHABs from 2011 to 2014 are the smallest in the last 20 years, which may be related to the large-scale planting of Eichhornia crassipes in the north of Dianchi Lake.     

Assessment of seasonal and year-to-year surface salinity signals retrieved from SMOS and Aquarius missions in the Bay of Bengal

The Bay of Bengal (BoB) exhibits a wide range of sea surface salinity (SSS), with very fresh water induced by heavy monsoonal precipitation and river run-offs to the north, and saltier water to the south. This is a particularly challenging region for the application of satellite-derived SSS measurements because of the potential pollution of the SSS signal by radio frequency interference (RFI) and land-induced contamination in this semi-enclosed basin. The present study validates recent level-3 monthly gridded (1° × 1°) SSS products from Soil Moisture and Ocean Salinity (SMOS) and Aquarius missions to an exhaustive in situ SSS product for the BoB. Current SMOS SSS retrievals do not perform better than existing climatologies. This is in stark contrast to Aquarius, which outperforms SMOS and available SSS climatologies everywhere in the BoB. While SMOS only captures the SSS seasonal evolution in the northern part of the Bay, Aquarius accurately captures the seasonal signal in the entire basin. The Aquarius product is also able to capture SSS non-seasonal anomalies, with an approximate correlation (r) of 0.75 with box-averaged in situ data in the northern, central, and western parts of the Bay. Aquarius can, thus, be confidently used to monitor large-scale year-to-year SSS variations in the BoB.     

Impacts of altimeter corrections on local linear sea level trends around Taiwan

Multi-mission altimeter measurements from TOPEX, Jason-1, and Jason-2 satellite altimetry over the 1993–2009 time span are used to characterize the local linear sea level trend (LSLT) around Taiwan. The results show that the long-term changes of default geophysical and range corrections, i.e. the inverted barometer correction, wet tropospheric correction, and sea state bias correction, have significant impacts on the determination of local LSLT. The trend of default corrections contribute more than 1.4 mm year^?1 along the coastline of China mainland and 2.1 mm year^?1 to local LSLT in the Taiwan Strait. The default-corrected altimetric data exhibit highest and lowest local LSLTs in the southeast and northwest of Taiwan, respectively. The regional LSLTs of 3.8 mm year^?1 and 4.6 mm year^?1 are estimated from the default-corrected and uncorrected altimetric data in the study area, respectively.     

Interpretation of Seasat radar-altimeter data over sea ice using near-simultaneous SAR imagery

Abstract

The backscatter properties of Seasat altimeter data in the Beaufort Sea on the 3 October 1978 show distinct zones, which arc interpreted in terms of geophysical characteristics. An overlapping and near-simultaneous synthetic-aperture radar image shows regions of open water, new ice and multi-year sea ice, which correspond to the different zones. It is found that the altimeter signal is sensitive to the ocean-ice boundary and that it indicates the ice type. The pulse-echo waveforms also suggest that several scattering components are present in the returned power over sea ice.     

Point or pointless – quality of ground data

A method for measuring continuously the inherent optical properties of water together with the salinity and the temperature values was developed and tested at the Division of Geophysics, University of Helsinki. The flow‐through system operates from a moving boat and has been used to collect parameters for optical modelling, coastal zone and inland water studies and to track the path of the fresh water spreading into sea areas. The system was also used in Lake Vänern, Sweden, to calculate the radiance reflectance, R _r, and total back‐scattering efficiency, b _{b eff}, along a transect. An example from the Gulf of Finland is presented, which shows how the spectral behaviour of light changes when moving away from a fresh water source. Data collected from the River Kymijoki estuary showed that the details in a rapidly changing environment were strongly smoothed in a Moderate Resolution Imaging Spectroradiometer (MODIS) data image. The correlation for continuously measured scattering values and MODIS channel 1 data varied between 0.70 and 0.85, n?=?126. Flow‐through measurement datasets can be used to obtain representative sites for vertical profiles or calibration measurements.     

Interannual variability in water storage over 2003-2008 in the Amazon Basin from GRACE space gravimetry, in situ river level and precipitation data

We investigate the interannual variability over 2003-2008 of different hydrological parameters in the Amazon river basin: (1) vertically-integrated water storage from the GRACE space gravimetry mission, (2) surface water level of the Amazon River and its tributaries from in situ gauge stations, and (3) precipitation. We analyze the spatio-temporal evolution of total water storage from GRACE and in situ river level along the Amazon River and its main tributaries and note significant differences between the various parts of the basin. We also perform an Empirical Orthogonal Decomposition of total water storage, river level and precipitation over the whole basin. We find that the 2003-2008 period, is characterized by two major hydrological events: a temporary drought in late 2005 that affected the western and central parts of the basin and very wet conditions peaking in mid-2006, in the eastern, northern and southern regions of the basin. Derivative of basin-average water storage from GRACE is shown to be highly correlated with the Southern Oscillation Index (a proxy of ENSO — El Niño-Southern Oscillation), confirming that the spatio-temporal change in hydrology of the Amazon basin is at least partly driven by the ENSO phenomenon, as noticed in previous studies.     

Whale rover moving along the surface of sperm whale

ABSTRACT

Biologging, which uses small data loggers directly attached to the bodies of animals to collect various behavioral data, can be an effective means for revealing the mysteries of animal life. With respect to marine animals, zoologists have attempted to obtain video data of a sperm whale eating a giant squid using biologging. These previous efforts have been unsuccessful because the biologger, which was attached to the whale's back that emerged from the sea as the whale swam, provided poor visibility of the whale's mouth area in the deep sea. To solve this problem, we proposed a novel roving biologger or whale rover that travels along a sperm whale's body surface from its back to its mouth area using robotic technology. Four prior whale rover prototypes have been designed and developed. In this study, we further improved the whale rover design to allow for adapted travel on curved or uneven surfaces. The feasibility of this fifth prototype was confirmed using both field and laboratory experiments. These experimental results demonstrated the whale rover's ability to successfully travel across a flat surface at a depth of almost 500 m and across a curved surface in a laboratory water tank.     

Seasonal and interannual variability of oceanographic processes in the Gulf of Guinea: An investigation using AVHRR sea surface temperature data

The Gulf of Guinea is situated in a critical position for understanding Atlantic equatorial dynamics. This study investigates seasonal and interannual variability in sea surface temperature (SST) throughout this region, focusing on dynamical ocean processes. A 10.5-year time series of remotely sensed SST data with 4 km spatial resolution from the Advanced Very High Resolution Radiometer (AVHRR) were used for this investigation, as they are sufficient to resolve shelf processes. Firstly, patterns of cloud cover were assessed, then spatio-temporal variability in SST patterns was investigated. Features identified in climatological SST images were the Senegalese upwelling influence, coastal upwelling, tropical surface water, river run-off and fronts. Of particular interest is a shelf-edge cooling along the coast of Liberia and Sierra Leone in February. Interannual variability, assessed using annual mean images, time series decomposition and spectral analysis, showed a quasi-cyclic pattern of warm and cool years, perhaps related to El Niño-type forcing. The results of this study show the usefulness of infrared remote sensing for tropical oceanography, despite high levels of cloud cover and atmospheric water vapour contamination, and they provide evidence for theories of westward movement of the upwelling against the Guinea current and remote forcing of the upwelling.     

Using NOAA AVHRR imagery in assessing water quality parameters

Abstract

The Advanced Very High Resolution Radiometer (AVHRR) instrument, carried by the NOAA-TIROS/N series of operational meteorological satellites can, on a routine basis, provide observational data which allow interpretation in terms of parameters related to water quality. In principle, some, though not all of the algorithms applied to Coastal Zone Colour Scanner data can be transformed for use with AVHRR observations. In combination with the operational character of the NOAA satellites this opens up the way to applications in monitoring of open sea and inland waters. Algorithms and results for some examples of such potential applications are presented.     

Application of a lidar fluorosensor system to the continuous and remote monitoring of the Southern Ocean and Antarctic Ross Sea: Results collected during the XIII and XV Italian oceanographic campaigns

A mobile fluorosensor laboratory, including as main constituent a lidar fluorosensor apparatus for remote measurements at water surface and ancillary instruments dedicated to local analyses, was developed for extensive biooptical monitoring of the sea waters. Continuous remote and local measurements of Chl-a (Chlorophyll a) and CDOM (Chromophoric Dissolved Organic Matter) were performed during the XIII (1997/1998) and XV (1999/2000) marine campaigns in the South-western Ross Sea and along the Southern Ocean transects to New Zealand as part of the Italian Research Programme for Antarctica. Chla and CDOM fluorescence maps of the investigated areas revealed the bio-optical peculiarity of coastal zones and seasonal changes encountered.     

Loss of terrestrial water storage in the Tianshan mountains from 2003 to 2015

ABSTRACT

The Tianshan Mountains region in Central Asia is covered with a large mass of glaciers and seasonal snow cover. This region supplies the main freshwater resources for Central Asia but has been severely affected by climate change over the past decades. In this study, we use the Gravity Recovery and Climate Experiment (GRACE) and Global Land Data Assimilation System (GLDAS) datasets to analyze the spatiotemporal variability of the terrestrial water storage (TWS) in the Tianshan Mountains from 2003 to 2015. The analysis shows that the TWS in the Tianshan Mountains has declined during the past decade. Seasonal changes in the water storage are caused by seasonal differences in the combined precipitation and temperature conditions. The results of TWS variations (TWSVs) in the Tianshan Mountains in 2003–2015 indicated that there is a declining rate of the TWS of the TWS-Mascon, TWS-Gaussian, and TWS-Noah is ?0.72, ?0.48, and ?0.41 cm year^?1, respectively. This suggests that the water storage loss in Tianshan Mountains has been about ?4.32 × 10⁹, ?2.88 × 10⁹, and ?2.46 × 10⁹ m³ year^?1 during 2003–2015, respectively. Glaciers and seasonal snow cover shrinkage obviously are the main factors governing the spatial difference in the TWSV. Annual mean temperature stays in a high state from the mid-1990s has been a predominant factor affecting the TWSV in the mountains during the past decade. A significant temperature increase in the middle region (Chinese part) accelerated the glacier and snow-cover shrinkage, which resulted in TWS loss.