Monday, July 22, 2013

Triton (gastropod)

Triton is the common name given in particular to a number of species of very large predatory sea snailsmarine gastropod mollusks in the genus CharoniaThe name "triton" is also often applied
as part of the common name, to much smaller sea snails of other genera within the same familyRanellidae.
TheCharonia tritonis (Linnaeus, 1758), which lives in the Indo-Pacific faunal zone, can grow to over half a metre(20 inches) in length.
shell of the giant triton 
One slightly smaller but still very large species, Charonia variegata (Lamarck, 1816), lives in the western Atlantic, from North Carolina to Brazil.

Tritons inhabit temperate and tropical waters worldwide.

Life habits
Unlike pulmonate and opistobranch gastropods, tritons are not hermaphrodites; they have separate sexes and undergo sexual reproduction with internal fertilization. The female deposits white capsules larvae. The larvae emerge free-swimming and enter the plankton, where they drift in open water for up to three months.
in clusters, each of which contains many developing 

Feeding behavior
Adult tritons are active predators and feed on other molluscs and starfish. The giant triton has gained fame for its ability to capture and eat crown-of-thorns starfish, a large species (up to one metre in diameter) covered in coral reef.
poisonous spikes an inch long. This starfish has few other natural predators and has earned the enmity of humans in recent decades by proliferating and destroying large sections of 
Tritons can be observed to turn and give chase when the scent of prey is detected. Some sea stars (including the crown-of-thorns starfish) appear to be able to detect the approach of the mollusk by means which are not clearly understood, and they will attempt flight before any physical contact has taken place. Tritons, however, are faster than sea stars and only larger starfish have a reasonable hope of escape, and then only by abandoning whichever limb the snail seizes first.
The triton grips its prey with its muscular foot and uses its toothy radula (a serrated, scraping organ found in gastropods) to saw through the sea star's armoured skin. Once it has penetrated, a paralyzing saliva subdues the prey and the snail feeds at leisure, often beginning with the softest parts such as the gonads and gut.
Tritons will ingest smaller prey animals whole without troubling to paralyse them, and will spit out any poisonous spines, shells or other unwanted parts later.

Human use
Many people find triton shells attractive as a design object, and so they are collected and sold as part of the international shell trade. In recent years this has contributed to the animals' scarcity.
From ancient times, people of many different cultures have removed the tip of the shell, or drilled a hole in the tip, and then used the shell as a trumpet.
The shell is well known as a decorative object, and is sometimes modified for use as a trumpet (such as the Japanese horagai).
C. tritonis is one of the few animals that feeds on the crown-of-thorns starfish, Acanthaster planci. Occasional plagues of this large and destructive starfish have killed extensive areas of coral on the Great Barrier Reef of Australia and the western Pacific reefs. There has been much debate on whether such plagues are natural or are caused by over-fishing of the few mollusks and fish that can eat this starfish. In 1994, Australia proposed that Charonia tritonis should be put on the CITES list, thereby attempting to protect the species.
Because of a lack of trade data concerning this seashell, the Berne Criteria from CITES were not met and the proposal was consequently withdrawn. While this species may be protected in Australia it can be legally traded and is found for sale in almost every shell shop in the world and on the Internet.

Friday, May 10, 2013


Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors (such as elevation). The word is derived from the Greek φαίνω (phainō), "to show, to bring to light, make to appear" + λόγος (logos), amongst others "study, discourse, reasoning" and indicates that phenology has been principally concerned with the dates of first occurrence of biological events in their annual cycle.
Examples include the date of emergence of leaves and flowers, the first flight of butterflies and the first appearance of 
migratory birds, the date of leaf colouring and fall in deciduous trees, the dates of egg-laying of birds and amphibia, or the timing of the developmental cycles of temperate-zone honey bee colonies. In the scientific literature on ecology, the term is used more generally to indicate the time frame for any seasonal biological phenomena, including the dates of last appearance (e.g., the seasonal phenology of a species may be from April through September).
Because many such phenomena are very sensitive to small variations in climate, especially to temperature, phenological records can be a useful proxy for temperature in historical climatology, especially in the study of climate change and global warming. For example, viticultural records of grape harvests in Europe have been used to reconstruct a record of summer growing season temperatures going back more than 500 years. In addition to providing a longer historical baseline than instrumental measurements, phenological observations provide high temporal resolution of ongoing changes related to global warming. The concept of Growing-degree day contributes to our understanding of phenology.

Past Record
Observations of phenological events have provided indications of the progress of the natural
calendar since ancient agricultural times. Many cultures have traditional phenological proverbs and sayings which indicate a time for action: "When the sloe tree is white as a sheet, sow your barley whether it be dry ash, 'Twill be a summer of wet and splash; If the ash is out before the oak,'Twill be a summer of fire and smoke." Theoretically, though, these are not mutually exclusive, as one forecasts immediate conditions and one forecasts future conditions.
or wet" or attempt to forecast future climate: "If oak's before ash, you're in for a splash. If ash before oak, you're in for a soak". But the indications can be pretty unreliable, as an alternative version of the rhyme shows: "If the oak is out before the 
The North American Bird Phenology Program at USGS Patuxent Wildlife Research Center (PWRC) is in possession of a collection of millions of bird arrival and departure date records for over 870 species across North America, dating between 1880 and 1970. This program, originally started by Wells W. Cooke, involved over 3,000 observers including many notable naturalists of the time. The program ran for 90 years and came to a close in 1970 when other programs starting up at PWRC took precedent. The program was again started in 2009 to digitize the collection of records and now with the help of citizens worldwide, each record is being transcribed into a database which will be publicly accessible for use.
The English naturalists Gilbert White and William Markwick reported the seasonal events of more than 400 plant and animal species, Gilbert White in Selborne, Hampshire and William Markwick in Battle, Sussex over a 25-year period between 1768 and 1793. The data, reported in White's Natural History and Antiquities of Selborne are reported as the earliest and latest dates for each event over 25 years; so annual changes cannot therefore be determined.
In Japan and China the time of blossoming of cherry and peach trees is associated with ancient festivals and some of these pinot noir grape in Burgundy have been used in an attempt to reconstruct spring–summer temperatures from 1370 to 2003; the reconstructed values during 1787–2000 have a correlation with Paris instrumental data of about 0.75.
dates can be traced back to the eighth century. Such historical records may, in principle, be capable of providing estimates of climate at dates before instrumental records became available. For example, records of the harvest dates of the 

Modern Record
Robert Marsham is the founding father of modern phenological recording. Marsham was a wealthy landowner who kept systematic records of "Indications of spring" on his estate at Stratton StrawlessNorfolk, from 1736. These were in the form of dates of the first occurrence of events such as flowering, bud burst, emergence or flight of an insect. Consistent records of the same events or
"phenophases" were maintained by generations of the same family over unprecedentedly long periods of time, eventually ending with the death of Mary Marsham in 1958, so that trends can be observed and related to long-term climate records. The data show significant variation in dates which broadly correspond with warm and cold years. Between 1850 and 1950 a long-term trend of gradual climate warming is observable, and during this same period the Marsham record of oak leafing dates tended to become earlier.
After 1960 the rate of warming accelerated, and this is mirrored by increasing earliness of oak leafing, recorded in the data collected by Jean Combes in Surrey. Over the past 250 years, the first leafing date of oak appears to have advanced by about 8 days, corresponding to overall warming on the order of 1.5°C in the same period.
Towards the end of the 19th century the recording of the appearance and development of plants and animals became a national pastime, and between 1891 and 1948 a programme of phenological recording was organised across the British Isles by the Royal Meteorological Society (RMS). Up to 600 observers submitted returns in some years, with numbers averaging a few hundred. During this period 11 main plant phenophases were consistently recorded over the 58 years from 1891-1948, and a further 14 phenophases were recorded for the 20 years between 1929 and 1948. The returns were summarised each year in the Quarterly Journal of the RMS as The Phenological Reports. The 58-year data have been summarised by Jeffree (1960), and show that flowering dates could be as many as 21 days early and as many as 34 days late, with extreme earliness greatest in summer flowering species, and extreme lateness in spring flowering species. In all 25 species the timings of all phenological events are significantly related to temperature indicating that phenological events are likely to get earlier as climate warms.
The Phenological Reports ended suddenly in 1948 after 58 years, and Britain was without a national recording scheme for almost 50 years, just at a time when climate change was becoming evident. During this period, important contributions were made by individual dedicated observers. The naturalist and author Richard Fitter recorded the First Flowering Date (FFD) of 557 species of British flowering plants in Oxfordshire between about 1954 and 1990. Writing in Science in 2002, Richard Fitter and his son Alistair Fitter found that "the average FFD of 385 British plant species has advanced by 4.5 days during the past decade compared with the previous four decades." They note that FFD is sensitive to temperature, as is generally agreed, that "150 to 200 species may be flowering on average 15 days earlier in Britain now than in the very recent past" and that these earlier FFDs will have "profound ecosystem and evolutionary consequences".
In the last decade, national recording in Britain has been resumed by the UK Phenology network, run by Woodland Trust and the Centre for Ecology and Hydrology and the BBC Springwatch survey. There is a USA National Phenology Network in which both professional scientists and lay recorders participate, a European Phenology Network that has monitoring, research and educational remits and many other countries such as Canada (Alberta Plantwatch and Saskatchewan PlantWatch), China and Australia have phenological programs.
In eastern North America, almanacs are traditionally used for information on action phenology (in agriculture), taking into account the astronomical positions at the time. William Felker has studied phenology in Ohio, USA since 1973 and now publishes "Poor Will's Almanack", a phenological almanac for farmers (not to be confused with a late 18th century almanac by the same name).

Airborne Sensors
Recent technological advances in studying the earth from space have resulted in a new field of phenological research that is concerned with observing the phenology of wholeecosystems and stands of vegetation on a global scale using proxy approaches. These methods complement the traditional phenological methods which recorded the first occurrences of individual species and phenophases.
The most successful of these approaches is based on tracking the temporal change of a Vegetation Index (like Normalized Difference Vegetation Index(NDVI)). NDVI makes use of the vegetation's typical low Infrared (Infrared energy is mostly reflected by plants due to their cellular structure). Due to its robustness and simplicity, NDVI has become one of the most popular remote sensing based products. Typically, a vegetation index is constructed in such a way that the attenuated reflected sunlight energy (1% to 30% of incident sunlight) is amplified by ratio-ing red and NIR following this equation:
reflection in the red (red energy is mostly absorbed by growing plants for Photosynthesis) and strong reflection in the Near 

\mathrm{NDVI}={\mathrm{NIR}-\mathrm{red} \over \mathrm{NIR}+\mathrm{red}}

The evolution of the vegetation index through time, depicted by the graph above, exhibits a strongcorrelation with the typical green vegetation growth stages (emergence, vigor/growth, maturity, and harvest/senescence). These temporal curves are analyzed to extract useful parameters about the vegetation growing season (start of season, end of season, length of growing season, etc.). Other growing season parameters could potentially be extracted, and global maps of any of these growing season parameters could then be constructed and used in all sorts of climatic change studies.
A noteworthy example of the use of remote sensing based phenology is the work of Ranga Myneni from Boston University. This work showed an apparent increase in vegetation productivity that most likely resulted from the increase in temperature and lengthening of the growing season in the boreal forest. Another example based on the MODIS enhanced vegetation index (EVI) reported by Alfredo Huete at the University of Arizona and colleagues showed that the Amazon Rainforest, as opposed to the long held view of a monotonous growing season or growth only during the wet rainy season, does in fact exhibit growth spurts during the dry season.
However, these phenological parameters are only an approximation of the true biological growth stages. This is mainly due to the limitation of current space based remote sensing, especially the spatial resolution, and the nature of vegetation index. A pixel in an image does not contain a pure target (like a tree, a shrub, etc.) but contains a mixture of whatever intersected the sensor's field of view.

Sunday, March 17, 2013

Marine radar

Marine radars are x-band or s-band radar to provide bearing and distance of ships and land targets in vicinity from own ship (radar scanner) for collision avoidance and navigation at sea.
Radar is a vital component for safety at sea and near the shore. Captains need to be able to maneuver theirs ships within feet in the worst of conditions and to be able to navigate "blind". This means inside a dark room with no visibility they need to safely navigate their way through waters in the worst of weather. Radars are rarely used alone in a marine setting. In commercial ships, they are integrated into a full system of marine instruments including chartplotterssonar, two-way radio communication devices, and emergency locators (EPIRB).
The integration of these devices is very important as it becomes quite distracting to look at several different screens. Therefore, displays can often overlay charting, radar, sonar into a single system. This gives the captain unprecedented instrumentation to maneuver the ship. With digital backbones, these devices have advanced greatly in the last years. For example, the newer ones have 3D displays that allow you to see above, below and all around the ship, including overlays of satellite imaging.
While private mariners are not subject to the same safety standards as commercial mariners, not having the correct electronics can lead to serious mishaps, including collisions with other vessels, running aground, running out of fuel and getting lost. It is very difficult to navigate waterways without navigation equipment and it is easy for a captain to get lost. You should have the correct equipment based on the size of your boat. This is not only for your safety but for the safety of others around you.
In port or in harbour, shore-based vessel traffic service radar systems are used to monitor and regulate ship movements in busy waters.

Collision avoidance
As required by COLREGS, all ships shall maintained a proper radar lookout if it is available on board to obtain early warning of risk of collision. Radar plotting or ARPA should be used to get the information of movement and the risk of collision (bearing, distance, CPA (closest point of approach), TCPA) of other ships in vicinity.

Marine radar systems can provide very useful radar navigation information for navigators onboard ships. Ship position could be fixed by the bearing and distance information of land target on radar screen.

Radar Controls
Marine radar has performance adjustment controls for brightness and contrast, gain, tuning, sea clutter and rain clutter suppression, and other interference reduction. Other common controls consist of range scale, bearing cursor, fix/variable range marker or bearing/distance cursor.

Radar Navigation
Marine and aviation radar systems can provide very useful navigation information in a variety of situations. When a vessel is within radar range of land or special radar aids to navigation, the navigator can take distances and angular bearings to charted objects and use these to establish arcs of position and lines of position on a chart. A fix consisting of only radar information is called a radar fix.
Some types of radar fixes include the relatively self-explanatory methods of "range and bearing to a single object," "two or more bearings," "tangent bearings," and "two or more ranges."
Parallel indexing is a technique defined by William Burger in the 1957 book The Radar Observer's Handbook. This technique involves creating a line on the screen that is parallel to the ship's course, but offset to the left or right by some distance. This parallel line allows the navigator to maintain a given distance away from hazards.
Some techniques have been developed for special situations. One, known as the "contour method," involves marking a transparent plastic template on the radar screen and moving it to the chart to fix a position.
Another special technique, known as the Franklin Continuous Radar Plot Technique, involves drawing the path a radar object should follow on the radar display if the ship stays on its planned course. During the transit, the navigator can check that the ship is on track by checking that the pip lies on the drawn line.
The Yeoman Plotter uses both radar, GPS and traditional charts to plot courses and is one of the most used plotters today.
After completing the plotting radar technique, the image from the radar can either be displayed, captured or recorded to a computer monitor using a frame grabber.

Navigation Processes
Day's work in navigation
The Day's work in navigation is a minimal set of tasks consistent with prudent navigation. The definition will vary on military and civilian vessels, and from ship to ship, but takes a form resembling:
  1. Maintain continuous dead reckoning plot.
  2. Take two or more star observations at morning twilight for a celestial fix. (prudent to observe 6 stars)
  3. Morning sun observation. Can be taken on or near prime vertical for longitude, or at any time for a line of position.
  4. Determine compass error by azimuth observation of the sun.
  5. Computation of the interval to noon, watch time of local apparent noon, and constants for meridian or ex-meridian sights.
  6. Noontime meridian or ex-meridian observation of the sun for noon latitude line. Running fix or cross with Venus line for noon fix.
  7. Noontime determination the day's run and day's set and drift.
  8. At least one afternoon sun line, in case the stars are not visible at twilight.
  9. Determine compass error by azimuth observation of the sun.
  10. Take two or more star observations at evening twilight for a celestial fix. (prudent to observe 6 stars)

Passage planning
Passage planning or voyage planning is a procedure to develop a complete description of vessel's voyage from start to finish. The plan includes leaving the dock and harbor area, the enroute portion of a voyage, approaching the destination, and mooring. According to international law, a vessel's captain is legally responsible for passage planning, however on larger vessels, the task will be delegated to the ship's navigator.
Studies show that human error is a factor in 80 percent of navigational accidents and that in many cases the human making the error had access to information that could have prevented the accident. The practice of voyage planning has evolved from penciling lines onnautical charts to a process of risk management.
Passage planning consists of four stages: appraisal, planning, execution, and monitoring, which are specified in International Maritime Organization Resolution A.893(21), Guidelines For Voyage Planning, and these guidelines are reflected in the local laws of IMO signatory countries (for example, Title 33 of the U.S. Code of Federal Regulations), and a number of professional books or publications. There are some fifty elements of a comprehensive passage plan depending on the size and type of vessel.
The appraisal stage deals with the collection of information relevant to the proposed voyage as well as ascertaining risks and assessing the key features of the voyage. In the next stage, the written plan is created. The third stage is the execution of the finalised voyage plan, taking into account any special circumstances which may arise such as changes in the weather, which may require the plan to be reviewed or altered. The final stage of passage planning consists of monitoring the vessel's progress in relation to the plan and responding to deviations and unforeseen circumstances.
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