Latitude Error Research Articles

Northern Range Limit of Opuntia fragilis and the Cactaceae is 56°N, Not 58°N

Two of the most used sources for distributions of cacti (Cactaceae) indicate the family's northern range limit is either 58°N or 58°15′N for Opuntia fragilis. However these sources overstate the range limit by almost two degrees, an error that probably originated as a simple misreading of the latitude of Fort St. John. I discuss records of O. fragilis at and just south of 56°17′ N along the Peace River valley between Fort St. John, British Columbia and Peace River, Alberta, as well as why it is surprising but unlikely that specimens currently exist farther north. An error in latitude of 2° (223 km) in range can adversely affect ability to empirically estimate effects of climate change.

Latitude Error in Compass Deviation: Mathematical Method to Determine the Latitude Error in Magnetic Compass Deviation

Abstract This article aims to provide the seafarer with a tool to calculate the deviation for a righted ship in any geographical position using only the information available on board. In this way the accidental errors in the deviation card are reduced and the latitude error is made negligible. Moreover, an experimental application of this method is carried out on board a tanker to compare the latitude error in different positions at sea.

Movements, dispersion, and mixing of bigeye tuna (Thunnus obesus) tagged and released in the equatorial Central Pacific Ocean, with conventional and archival tags

A total of 31,242 bigeye tuna was captured, tagged, and released, 30,793 with dart tags (DTs) and 449 with geolocating archival tags (ATs), in the equatorial central Pacific Ocean along the 140° W, 155° W, 170° W, and 180° meridians, during 2008 through 2012, of which 10,029 (32.1%) of the DTs and 74 (16.5%) of the ATs were returned. A subset of high-confidence filtered DT data was retained for 5807 fish at liberty for 30d or more, for evaluating linear displacements from release to recapture positions. For the filtered DT data, days at liberty ranged from 30 to 1701d (median=187 d). Linear displacements ranged from 1 to 5372 nautical miles (M) (median=936M), with 71% eastward and 29% westward, and 95% within 3614M of their release positions. The data indicate significant differences in the linear displacements by release locations, days at liberty, and fish length at release. An unscented Kalman filter model with sea-surface temperature measurements integrated (UKFsst) was used to process 48 AT data sets from bigeye tuna at liberty for 30d or longer, to obtain most probable tracks, improved estimates of geographic positions, and movement parameters. The 95% volume contours surrounding the position estimates, along the most probable tracks from bigeye tuna releases along the 140° W, 155° W, 170° W, and 180° meridians show substantial overlap. For the pooled AT data sets, the median parameter estimates from the UKFsst model for errors in longitude (σx) and latitude (σy) were 0.52° and 1.75°, for directed eastward and northward movements (u and v) were −2.01M/d and −1.41M/d, and for dispersive movement (D) was 496.7M2/d. The linear displacements and most probable tracks obtained from these tagging data demonstrate constrained latitudinal dispersion, some regional fidelity, some extensive eastward longitudinal dispersion, and substantial mixing of bigeye tuna between release longitudes. The amount of mixing of bigeye tuna among these release areas in the equatorial central Pacific Ocean, with those in adjacent areas of the equatorial eastern and western Pacific Ocean, is dependent on distances between areas, with, in general, the greatest mixing occurring between the areas that are closest to one another.

A Two-Mode INS/CNS Navigation Method for Lunar Rovers

A secure and autonomous navigation system is needed for the lunar rover in future lunar missions. The inertial navigation system (INS) and celestial navigation system (CNS) are two usually used autonomous navigation systems for rovers. Because INS and CNS are complementary to each other, INS/CNS integrated navigation becomes a very attractive solution for long-time and long-distance navigation. Traditional INS/CNS methods for aircrafts or ballistic missiles are not optimal for rovers because these methods only work in one motion state, but the rover operates in two motion states. For solving this problem, a two-mode INS/CNS navigation method for lunar rovers is presented in this paper. When the rover is stationary, a tightly coupled mode is used to correct the position and attitude of the rover. When the rover is in motion, a loosely coupled mode is used to correct the attitude of the rover. Two modes use different system models and different measurements to fulfill different targets and keep the error of position and attitude from accumulation. The validity and feasibility of the two-mode method is tested and examined by ground test system. The longitude and latitude errors within 50 m in distance can be achieved by this two-mode method during an 80-min traverse. These results demonstrate that it is a good choice of autonomous and high-accuracy navigation for lunar rovers.

Error Analysis and Compensation of Gyrocompass Alignment for SINS on Moving Base

An improved method of gyrocompass alignment for strap-down inertial navigation system (SINS) on moving base assisted with Doppler velocity log (DVL) is proposed in this paper. After analyzing the classical gyrocompass alignment principle on static base, implementation of compass alignment on moving base is given in detail. Furthermore, based on analysis of velocity error, latitude error, and acceleration error on moving base, two improvements are introduced to ensure alignment accuracy and speed: (1) the system parameters are redesigned to decrease the acceleration interference and (2) a data repeated calculation algorithm is used in order to shorten the prolonged alignment time caused by changes in parameters. Simulation and test results indicate that the improved method can realize the alignment on moving base quickly and effectively.

Movements, behavior, and habitat utilization of yellowfin tuna (Thunnus albacares) in waters surrounding the Revillagigedo Islands Archipelago Biosphere Reserve, Mexico

AbstractThe movements, behavior, and habitat utilization of yellowfin tuna, Thunnus albacares, following capture and release with archival tags in the Revillagigedo Islands Archipelago Biosphere Reserve (RIABR), Mexico, are described from analyses of 16 578 days of time‐series data, downloaded from 52 archival tags recovered from yellowfin (78–173 cm in length and 1.7–8.0 yr of age) at liberty from 93 to 1773 days ( = 411 days), collected during 2006–2012. An unscented Kalman filter model with sea‐surface temperature measurements integrated (UKFsst) was used to process the archival tag data sets to obtain improved estimates of geographic positions, most probable tracks (MPTs), and movement parameters. The MPTs indicate restricted movements, low levels of dispersion, and fidelity of yellowfin tuna to the RIABR. The median parameter estimates from the UKFsst model for errors in longitude (σx) and latitude (σy) were 0.46° and 1.84°, respectively, for directed movements (u and v) –0.05 NM day−1 and –0.05 NM day−1, respectively, and for dispersive movement (D) 117.99 NM2 day−1. Analyses of daily timed depth and temperature records resulted in the classification of the data into four distinct behaviors. There are significant differences among ages in the durations of Type I and Type II diving behaviors and in the daytime and nighttime vertical habitat utilization distributions. The oceanography surrounding the RIABR appears to have a profound influence on the movements, behavior, and habitat utilization of yellowfin in this area.

Error Properties of Argos Satellite Telemetry Locations Using Least Squares and Kalman Filtering

Study of animal movements is key for understanding their ecology and facilitating their conservation. The Argos satellite system is a valuable tool for tracking species which move long distances, inhabit remote areas, and are otherwise difficult to track with traditional VHF telemetry and are not suitable for GPS systems. Previous research has raised doubts about the magnitude of position errors quoted by the satellite service provider CLS. In addition, no peer-reviewed publications have evaluated the usefulness of the CLS supplied error ellipses nor the accuracy of the new Kalman filtering (KF) processing method. Using transmitters hung from towers and trees in southeastern Peru, we show the Argos error ellipses generally contain <25% of the true locations and therefore do not adequately describe the true location errors. We also find that KF processing does not significantly increase location accuracy. The errors for both LS and KF processing methods were found to be lognormally distributed, which has important repercussions for error calculation, statistical analysis, and data interpretation. In brief, “good” positions (location codes 3, 2, 1, A) are accurate to about 2 km, while 0 and B locations are accurate to about 5–10 km. However, due to the lognormal distribution of the errors, larger outliers are to be expected in all location codes and need to be accounted for in the user’s data processing. We evaluate five different empirical error estimates and find that 68% lognormal error ellipses provided the most useful error estimates. Longitude errors are larger than latitude errors by a factor of 2 to 3, supporting the use of elliptical error ellipses. Numerous studies over the past 15 years have also found fault with the CLS-claimed error estimates yet CLS has failed to correct their misleading information. We hope this will be reversed in the near future.

Location Performance and Detection Threshold of the Spanish National Seismic Network

Spain is a low-to-moderate seismicity area with relatively low seismic hazard. However, several strong shallow earthquakes have shaken the country causing casualties and extensive damage. Regional seismicity is monitored and surveyed by means of the Spanish National Seismic Network, maintenance and control of which are entrusted to the Instituto Geografico Nacional. This array currently comprises 120 seismic stations distributed throughout Spanish territory (mainland and islands). Basically, we are interested in checking the noise conditions, reliability, and seismic detection capability of the Spanish network by analyzing the background noise level affecting the array stations, errors in hypocentral location, and detection threshold, which provides knowledge about network performance. It also enables testing of the suitability of the velocity model used in the routine process of earthquake location. To perform this study we use a method that relies on P and S wave travel times, which are computed by simulation of seismic rays from virtual seismic sources placed at the nodes of a regular grid covering the study area. Given the characteristics of the seismicity of Spain, we drew maps for M L magnitudes 2.0, 2.5, and 3.0, at a focal depth of 10 km and a confidence level 95 %. The results relate to the number of stations involved in the hypocentral location process, how these stations are distributed spatially, and the uncertainties of focal data (errors in origin time, longitude, latitude, and depth). To assess the extent to which principal seismogenic areas are well monitored by the network, we estimated the average error in the location of a seismic source from the semiaxes of the ellipsoid of confidence by calculating the radius of the equivalent sphere. Finally, the detection threshold was determined as the magnitude of the smallest seismic event detected at least by four stations. The northwest of the peninsula, the Pyrenees, especially the westernmost segment, the Betic Cordillera, and Tenerife Island are the best-monitored zones. Origin time and focal depth are data that are far from being constrained by regional events. The two Iberian areas with moderate seismicity and the highest seismic hazard, the Pyrenees and Betic Cordillera, and the northwestern quadrant of the peninsula, are the areas wherein the focus of an earthquake is determined with an approximate error of 3 km. For M L 2.5 and M L 3.0 this error is common for almost the whole peninsula and the Canary Islands. In general, errors in epicenter latitude and longitude are small for near-surface earthquakes, increasing gradually as the depth increases, but remaining close to 5 km even at a depth of 60 km. The hypocentral depth seems to be well constrained to a depth of 40 km beneath the zones with the highest density of stations, with an error of less than 5 km. The M L magnitude detection threshold of the network is approximately 2.0 for most of Spain and still less, almost 1.0, for the western sector of the Pyrenean region and the Canary Islands.

Movements, behavior, and habitat utilization of yellowfin tuna ( Thunnus albacares) in the Pacific Ocean off Baja California, Mexico, determined from archival tag data analyses, including unscented Kalman filtering

The movements, behavior, and habitat utilization of yellowfin tuna, Thunnus albacares, in the eastern Pacific Ocean off Baja California, Mexico, are described from analyses of 31,357 days of day-log and 28,835 days of time-series data, downloaded from 126 archival tags recovered from yellowfin (57–162 cm in length and 1.2–5.2 years of age) at liberty from 90 to 1161 d ( x ¯ = 273.2 d ), collected during 2002–2010. An unscented Kalman filter model with sea-surface temperature measurements integrated (UKFsst) was used to process the archival tag data sets in order to obtain improved estimates of geographic positions and most probable tracks (MPTs) and parameters. The median parameter estimates from the UKFsst model for errors in longitude ( σ x ) and latitude ( σ y ) were 0.32° and 1.36°, respectively, for directed movements ( u and v) were 0.27 and 0.77 nm/d, respectively, and for dispersive movement ( D) was 144.3 nm 2/d. The MPTs for 120 (95%) of the yellowfin remained within 1358 km of their release locations, indicating restricted horizontal utilization distributions, and fidelity to this area of high biological productivity. There are observed differences in the movement patterns and parameters for fish released in different areas. Analyses of daily timed depth and temperature records resulted in the classification of the data into four distinct behaviors. When exhibiting type-1 diving behavior (82.9% of all days at liberty) the fish remained at depths of less than 50 m at night and did not dive to depths greater than about 100 m during the day. Type-2 diving behavior (17.1% of all days at liberty) was characterized by 10 or more dives in excess of 150 m during the day. Spatial and temporal patterns are evident in the distributions of type-1 and type-2 diving behaviors. Surface-oriented behavior, defined as the time fish remained at depths less than 10 m for more than 10 min, was also evaluated. The mean number and duration of daytime surface-oriented events per day, for all fish, were 7.6 and 24.2 min, respectively. There are significant differences among ages in the percentages of days classified as type-1 and type-2 behaviors, durations of those events, and in the numbers and durations of surface-oriented events. Yellowfin tuna exhibited occasional deep-diving behavior, and some dives were to depths exceeding 1000 m, where ambient temperatures were less than 5 °C. There are significant differences among ages in the nighttime and daytime average depths. The differences are the result of the fish of ages greater than 3 years showing greater daytime average depths and lesser nighttime average depths.

Investigating Behaviour and Population Dynamics of Striped Marlin (Kajikia audax) from the Southwest Pacific Ocean with Satellite Tags

Behaviour and distribution of striped marlin within the southwest Pacific Ocean were investigated using electronic tagging data collected from 2005–2008. A continuous-time correlated random-walk Kalman filter was used to integrate double-tagging data exhibiting variable error structures into movement trajectories composed of regular time-steps. This state-space trajectory integration approach improved longitude and latitude error distributions by 38.5 km and 22.2 km respectively. Using these trajectories as inputs, a behavioural classification model was developed to infer when, and where, ‘transiting’ and ‘area-restricted’ (ARB) pseudo-behavioural states occurred. ARB tended to occur at shallower depths (108±49 m) than did transiting behaviours (127±57 m). A 16 day post-release period of diminished ARB activity suggests that patterns of behaviour were affected by the capture and/or tagging events, implying that tagged animals may exhibit atypical behaviour upon release. The striped marlin in this study dove deeper and spent greater time at ≥200 m depth than those in the central and eastern Pacific Ocean. As marlin reached tropical latitudes (20–21°S) they consistently reversed directions, increased swimming speed and shifted to transiting behaviour. Reversals in the tropics also coincided with increases in swimming depth, including increased time ≥250 m. Our research provides enhanced understanding of the behavioural ecology of striped marlin. This has implications for the effectiveness of spatially explicit population models and we demonstrate the need to consider geographic variation when standardizing CPUE by depth, and provide data to inform natural and recreational fishing mortality parameters.

A Non-singular Horizontal Position Representation

Position calculations, e.g. adding, subtracting, interpolating, and averaging positions, depend on the representation used, both with respect to simplicity of the written code and accuracy of the result. The latitude/longitude representation is widely used, but near the pole singularities, this representation has several complex properties, such as error in latitude leading to error in longitude. Longitude also has a discontinuity at ±180°. These properties may lead to large errors in many standard algorithms. Using an ellipsoidal Earth model also makes latitude/longitude calculations complex or approximate. Other common representations of horizontal position include UTM and local Cartesian ‘flat Earth’ approximations, but these usually only give approximate answers, and are complex to use over larger distances. The normal vector to the Earth ellipsoid (called n-vector) is a non-singular position representation that turns out to be very convenient for practical position calculations. This paper presents this representation, and compares it with other alternatives, showing that n-vector is simpler to use and gives exact answers for all global positions, and all distances, for both ellipsoidal and spherical Earth models. In addition, two functions based on n-vector are presented, that further simplify most practical position calculations, while ensuring full accuracy.

An iterative algorithm to compute geodetic coordinates

By using the Newton–Raphson method to solve a quartic equation of the Lagrange parameter, we propose a new iterative algorithm for the transformation from Cartesian to geodetic coordinates. Numerical experiments show that the new method is sufficiently precise and free from singularity and non-convergency, except within 50 km of the geocentre. After one iteration, the maximum error of latitude is less than 10 −8 arc-sec and the relative height error is less than 10 −15 over the range of geodetic heights from −10 6 to 10 12 m. Comparisons of the complexity and performance with some other well-known methods indicate that the algorithm is efficient and accurate.

Fusion of GPS, Compass, and Camera for Localization of an Intelligent Vehicle

This paper proposes a fuzzy based sensor fusion algorithm for localization of an intelligent vehicle by correcting translational error of latitude and longitude in easily available maps such as Google Earth. Even though the chosen map possesses translational error, the proposed algorithm will automatically correct and compensate this error by using the integration of a Global Positioning System (GPS), a magnetic compass, and a CCD camera. To integrate these sensors, all the sensing data must be converted to the same reference. The GPS and the magnetic compass provide global data, whereas the camera provides local data. Since all sensors contain some uncertainties, the outputs of all sensors can be expressed by fuzzy numbers with triangular membership functions. All the fuzzy numbers are operated based on the alpha-cut closed interval properties. The proposed algorithm uses information from the GPS and the magnetic compass to calculate the global position of two selected pixels in two different segments, which represent road center line in the road images. Consequently, by knowing the global positions of the selected pixels, it is possible to calculate the horizontal and vertical deviations that the waypoints in the original map are to shift. The system performs efficiently on an unmarked road inside Asian Institute of Technology Thailand (AIT) campus.

Error Analysis Of Clock Time (T), Declination (*) And Latitude (Φ) On Astronomic Azimuth In Minna, Using Sun Altitude And Hour Angle Methods

The major end results of field and geodetic astronomy in surveying include time (t), latitude (&#934;), longitude (&#955;) and azimuth (A); which are aimed at establishing fixed positions and orientations of survey points and lines on the earth surface. The paper attempts the analysis of the individual and combined effects of error in time (t), declination (&#948;) and latitude (&#934;) on the computed azimuths (A) using the methods of altitude and hour angle of the sun, in Minna. The actual mean azimuth of the baseline (LS2K1 – P2) in a classical field observation procedure in both methods were 344° 32' 29.1” and 344° 32' 29.7” respectively. Deliberate observation and interpolation errors in the three parameters (t, &#948; and &#934;) were made in order to evaluate their individual and combined effects on the azimuth determinations respectively. In the sun altitude method, it was discovered that timing error of 10 min resulted in 7.6” error in the interpolation of declination, which in turn yielded error of about 9.9” in the computed azimuth (A). Also, declination interpolation of declination, which in turn yielded error of about 13” in the computed azimuth, and error of 10” in the scaled latitude resulted in error of 5.2” in the computed azimuth. Therefore, the combined error effects of 10” error in declination and latitude respectively (dA) on the computed azimuth was about 18.2”. In the hour angle method, it was observed that error in timing of about 56 seconds caused error in the computed azimuth of up to 53” of arc. An error of 6” in declination caused error of 3” in the computed azimuth, while error of 5” in latitude caused corresponding error of about 3” in the computed azimuth. Time is therefore a major factor in hour angle method despite the fact that it is not directly used in the equation for the azimuth computation. The multiple regression analysis of the variables shows a positive statistical significance of 99.8% in the relationship between dependent variable (A) and independent variables (t, &#948; and &#934;). It is recommended that to avoid unnecessary errors prior and post astronomical survey and analysis, sincerity of purpose and data integrity must be ensured. JORIND Vol. 5 (1) 2007: pp. 144-151

A NEW LOCATION OF TADPOLE SHRIMP (TRIOPS CANCRIFORMIS L.) IN LITHUANIA

Tadpole shrimps (Triops cancriformis L.) were registered on 10 August 2007 and during the repeated observation on 8 September 2007 (Fig. 1). Only two habitats of this species of triops are known to exist in Lithuania (Raðomavieius 2007). To date no records of T. cancriformis have been reported from the northern part of Lithuania (Raðomavieius 2007). The habitat of these rare crustaceans (Red Data Book of Lithuania category 2 (V), MoE 2007) has formed in quite an unexpected place – at the sodden edge of a rape field situated at a distance of 5.5 m from the carriageway side (Fig. 2). From the viewpoint of administrative division, the habitat of Triops cancriformis L. is in Pasvalys region, on the left side of the No. 150 motorway (Ðiauliai–Pakruojis–Pasvalys), 59.7 km from Ðiauliai. The nearest settlement Meðkalaukis lies 3.70 km south-west of the location. Coordinates of the location are 24°16'11.2'' east longitude and 56°01'53.0'' north latitude (error – 6 m). In the north of the habitat there is a 150 m wide tract of a rape field with a mediumaged mixed forest behind it. Approximately 50 m east of the habitat, there is a mature deciduous forest and a wheat field (Triticum sp. L.) to the south of it (on the other side of the above mentioned motorway). Suitable conditions for the development of T. cancriformis in the rape field formed for several reasons, water accumulation being of the primary importance. The location is situated in the lowland of central Lithuania, in a moderate descent of the flat landscape relief, just 41 m above sea level. However, the presumption that the habitat is supplied with groundwater has to be ruled out, for 45 m north-east of the site there is a ~10 m wide and ~5 m deep drain ditch which drains underground water. The only source of moisture for this temporary water body is precipitation. Thus, the second prerequisite for the formation of the T. cancriformis habitat comes out. It is specificity of soil. According to Miliauskas and Nedzinskas (2000), soils in these areas are periodically dry. Hence, soil moisture regime is mainly preconditioned by the amount of precipitation. Surface layers of carbonate-rich morenic clay loam and clay have formed a natural hydrological barrier (Galvydyte 2000). In 2007 the amount of precipitation was sufficient for the formation of a perennial puddle and develoment of T. cancriformis eggs. The fact that a number of water plants, plants of damp sites and algae managed to root and even to flourish there – some of them reaching generative and senile stages, proves that the terrain has been sodden for a long period of time (Vilkonis 2001). Among such plants the following should be mentioned: great reedmace (Typha latifolia L.), common reed-grass (Phragmites australis (Cav.) Trin. Ex Steud.), marsh woundwort (Stachys palustris L.), murr marigold (Bidens tripartita L.), marsh cranesbill (Geranium palustre L.), common water-plantain (Alisma plantagoaquatica L.), common mudwort (Limosella aquatica L.), muskgrasses (Chara sp.) (Gudþinskas 1999; Vilkonis 2001). The following water animals managed to inhabit the temporary water reservoir: pond scatter (Gerris sp.), great diving beetle (Dytiscus marginalis L.), and a lot of fire-bellied toads (Bombina bombina L.).

Interannual variation in large-scale movement of Atlantic bluefin tuna (Thunnus thynnus) determined from pop-up satellite archival tags

Data from pop-up satellite archival tags (PSATs) deployed on Atlantic bluefin tuna (Thunnus thynnus) in 1999, 2000, and 2002 were analyzed synthetically using variants of a state–space statistical model to estimate tag shedding positions, in situ position estimation errors, and movement parameters. Geographic position estimates were computed from PSAT data for 30% to 50% of the days at liberty for each tag. Such relatively low position reporting rates may present biased impressions of movement for brief times at liberty. The respective longitude and latitude errors were estimated by the state–space Kalman filter model to be approximately 0.4° and 1.0° for the 1999 deployments, 0.4° and 2.1° for the 2000 deployments, and 0.9° and 2.1° for the 2002 deployments. Estimated movement parameters were used in stochastic simulation models to predict the distribution of tagged fish after times at liberty that exceed observed reporting dates. The distributions predicted by parameters estimated from the 2002 deployments were more restricted than those estimated from the 1999 deployments. Atlantic bluefin dispersal patterns appear to be age- or size-dependent and linked to shifts in oceanographic conditions. Future fisheries management measures should address interannual differences in stock distribution identified by electronic tags.

Ionospheric effects on GPS positioning

Ionospheric scintillation results from a single frequency global positioning system (GPS) receiver have been presented in this paper. Ionospheric scintillation is rapid variation in the amplitude and phase of radio signals caused by irregularities in the ionosphere. Ionosphere contains large amplitude variations over spatial scales from few cm to 100s of km. It is observed that VHF–UHF communications as well as automated navigation and precision positioning via GPS are affected by scintillations. Scintillations do not have major effects on mid latitude regions, but low latitude scintillations are the greatest cause of GPS position errors. In the present work, we study the effect of ionospheric scintillations on GPS signal at low latitude station, Chiang Rai, Thailand. The data were analyzed from January 2001 to December 2001. Results show that scintillation has a significant problem at this latitude and position error increases during active scintillation condition, which causes loss of lock on several satellites.

Refinements in the use of equivalent latitude for assimilating sporadic inhomogeneous stratospheric tracer observations, 1: Detecting transport of Pinatubo aerosol across a strong vortex edge

Abstract. The use of PV equivalent latitude for assimilating stratospheric tracer observations is discussed - with particular regard to the errors in the equivalent latitude coordinate, and to the assimilation of sparse data. Some example measurements are assimilated: they sample the stratosphere sporadically and inhomogeneously. The aim was to obtain precise information about the isentropic tracer distribution and evolution as a function of equivalent latitude. Precision is important, if transport across barriers like the vortex edge are to be detected directly. The main challenges addressed are the errors in modelled equivalent latitude, and the non-ideal observational sampling. The methods presented allow first some assessment of equivalent latitude errors and a picture of how good or poor the observational coverage is. This information determines choices in the approach for estimating as precisely as possible the true equivalent latitude distribution of the tracer, in periods of good and poor observational coverage. This is in practice an optimisation process, since better understanding of the equivalent latitude distribution of the tracer feeds back into a clearer picture of the errors in the modelled equivalent latitude coordinate. Error estimates constrain the reliability of using equivalent latitude to make statements like "this observation samples air poleward of the vortex edge" or that of more general model-measurement comparisons. The approach is demonstrated for ground-based lidar soundings of the Mount Pinatubo aerosol cloud, focusing on the 1991-92 arctic vortex edge between 475-520K. Equivalent latitude is estimated at the observation times and locations from Eulerian model tracers initialised with PV and forced by UK Meteorological Office analyses. With the model formulation chosen, it is shown that tracer transport of a few days resulted in an error distribution that was much closer to Gaussian form, although the mean error was not significantly affected. The analysis of the observations revealed a small amount of irreversible transport of aerosol across the vortex edge during late January 1992, coincident with a strongly disturbed vortex.

ASSESSMENT OF ARGOS LOCATION ACCURACY FROM SATELLITE TAGS DEPLOYED ON CAPTIVE GRAY SEALS

AbstractThe Argos satellite system is commonly used to track and relay behavioral data from marine mammals, but their underwater habit results in a high proportion of locations of non‐guaranteed accuracy (location classes (LC) O, A, and B). The accuracy of these locations is poorly documented in marine mammals. We assessed the accuracy of all LCs on four juvenile gray seals fitted with Argos satellite relay data loggers and held in captivity in an outdoor tank for a total of 61 seal‐days. Four hundred and twenty‐six locations were obtained from seals in captivity, and their latitude and longitude error was assessed before and after filtering, following MConnell et al. (1992). There was significantly more error in longitude than latitude in all LCs except I. C A. The ratio of the standard deviations of longitude : latitude ranged from 1.77 (LC 3) to 2.58 (LC 1). Filtering had very little effect on errors in LCs 3‐1, but in the remaining LCs filtering resulted in error reductions ranging from 8% to 63%. In LCs O, A, and B, error reduction was greater in the 95th percentile errors, especially in longitude. The averages of the latitude and longitude 68th percentile errors and those predicted by Argos (in brackets) were 226 (150), 372 (350), and 757 (1000) m for LCs 3, 2, and 1 respectively. Both latitude and longitude errors of LCs &gt; O were normally distributed. Both filtered and unfiltered LC A locations were of a similar accuracy to LC 1 locations, and considerably better than LC O locations.

Archaeoastronomical orientation errors:The case of the two Hellenic pyramidals

In archaeoastronomical orientation purposes, employing appropriate software, the star declination (D) is determined from the geographical coordinates of the site, the plate bearing of the horizon point (azimuth, Az), and the altitude of the horizontal point (skyline), with appropriate corrections. Errors to the second of a degree in latitude have not any apparent effect on D, errors in Az and latitude of the skyline, however, transmit significant respective percentage errors in D. This note discusses the impact of such error variation on all parameters involved in archaeoastronomical orientation, and presents the case of two small sized pyramidals in Greece.