A NOTE ON THE CALCULATION OF POSITION LINES

Abstract

Since the computation of a set of star observations generally takes far longer than the actual observing, the method used in computing the results should be carefully chosen in those cases where a choice exists. The calculation of Position Lines is such a case.     

DETERMINATION OF AZIMUTH AND LATITUDE FROM OBSERVATIONS OF A SINGLE UNKNOWN STAR BY A NEW METHOD

Abstract

The purpose of this paper is to describe a new and easy method of determining the (astronomical) latitude and azimuth at any place and to explain the line of approach and the formulae. It will be seen that the method should be useful to a wide circle of land surveyors. One of its principal advantages is that identification of the star is not necesssary and it can be used when no star chart or star catalogue is available.     

A STELLAR PROGRAMME FOR TIME OBSERVATIONS

Abstract

A GOOD deal of astronomical work was called for during the operations of the British Somaliland–Ethiopia Boundary Commission. The method employed by the British Section for the determination of local time being that of star altitudes in the prime vertical, after the first few stations had been occupied the suggestion was made that the observer could be saved considerable strain by the preparation of a programme for time observations, much on the same lines as for latitudes. The proposal was tried, proved eminently successful, and became a standard part of the British Section's procedure. An example of such a programme is given below. I t is a little laborious, but simple.     

THE CURVATURE CORRECTION IN PRECISE AZIMUTH OBSERVATIONS UPON A CLOSE CIRCUMPOLAR STAR AT ANY HOUR ANGLE

Abstract

One method of reducing a series of pointings taken upon a close circumpolar star is to average the recorded horizontal angles and to obtain the average of the separate star azimuths by applying a curvature correction to the azimuth calculated from the average of the hour angles of the various pointings.     

ASTRO FIX BY TWO EX-MERIDIAN STARS

Abstract

DR. DE GRAAFF-HUNTER proposed two new astronomical methods in a paper which he read at the Conference of Commonwealth Survey Officers, and the writer recently had an opportunity of trying out one' of these, with some interesting results. The method used, which requires timed intersections on a pair of stars in azimuths differingby about 90° and depends upon the alg'ebraic solution of the pair of position lines so formed*, will yield latitude, longitude and azimuth. The observations are brief and uncomplicated, prior identification unnecessary",and ~4e subsequent. computation is light: and requires no more than about thirty minutes for a pair of stars, inclusive of star identification.     

ON OBSERVATIONS AND ADJUSTMENT

Abstract

The subdivision of methods of adjustment of observations as given in textbooks is usually asfollows: (1) The method of direct observations; (2) The method of indirect observations; (3) The method of conditioned observations.     

Shallow-water loading tides in Japan from superconducting gravimetry

Gravity observations from superconducting gravimeters are used to observe loading effects from shallow-water tides on the Japanese east and west coasts. Non-linear third-diurnal and higher-frequency shallow-water tides are identified in the tide-gauge observations from these coastal areas. The most energetic constituents in the tide gauge observations are also seen in the gravity observations due to their loading effects on the deformation of the Earth. Even though the shallow-water tides at the Japanese east coast have an amplitude of only a few millimetres, they are still able to generate a loading signal at gravity sites located several hundred kilometres inland. In particular, the S₃, S₄ and S₅ solar tides occur in both gravity and tide gauge observations. It is indicated that in other shelf regions with large shallow water tides, the shallow water loading signals account for a significant signal, which should be taken into account.Acknowledgement The authors would like to thank the Hydrographic and Oceanographic Department (Japan Coast Guard), Japan Meteorological Agency and Hokkaido Development Agency for access to the tide-gauge data. Also, the Global Geodynamic Project Information System and Data Center (GGP-ISDC) is acknowledged for providing the gravity data.     

OBSERVING POLARIS IN DAYLIGHT

Abstract

For azimuth and latitude it is a great advantage to observe Polaris in daylight as it eliminates torches and lamps. The following describes a rule of thumb method of finding the hour angle and a diagram to find the, altitude from the R.A. The altitude is then set on the vertical circle and, by moving the telescope a few degrees about the meridian (by compass), Polaris can easily be spotted near the centre of the field. The telescope must be focussed at infinity. After finding the star, the rigorous observations must be carriéd out.     

ANGLO-ETHIOPIAN (SOMALILAND) BOUNDARY COMMISSION, 1932-5

Abstract

Azimuth.—The method was that of star altitudes in the prime vertical, except at X. 34 where hour angles on the P.V. were observed. At B.P. 79 and 99, NE. Terminal, and X. 12 and 34, the measures were made by Major Godfrey-Faussett or Capt. Taylor with the 8-inch C.T. & S. micrometer theodolite; and at all other stations by Capt. Taylor with the Tavistock theodolite Y. 2304.     

Field Techniques in Remote Sensing: Learning by Doing

Abstract

The paper summarizes one professor's observations and resulting approach to teaching a semester‐long course on the subject of field techniques as they relate to remote‐sensing campaigns. The text describes how a “learning‐by‐doing strategy” is applied to such a course. More specifically, the paper describes how the instructor requires students to design, construct, and actually implement “hardware solutions” to problems involving collection of spectral (and ancillary) data in the field. Pupils must test their developed methodologies and “technological creations” with regard to a focused research problem undertaken in a difficult field setting during a week‐long outdoor experience. The students are expected to evaluate, and possibly modify, their methods and procedures “on‐the‐fly.” Individual group research problems, methods, and hardware solutions are briefly described, and selected student evaluations of the experience are provided.     

A statistical filter for geodetic observations

A method for filtering of geodetic observationwhich leaves the final result normally distributed, is presented. Furthermore, it is shown that if you sacrifice100.a% of all the observations you may be (1−β).100% sure that a gross error of the size Δ is rejected. Another and, may be intuitively, more appealing method is presented; the two methods are compared and it is shown why Method 1 should be preferred to Method 2 for geodetic purposes. Finally the two methods are demonstrated in some numerical examples.     

THE CALCULATION OF THE HEIGHT OF KILIMANJARO

Abstract

The observations to height Kilimanjaro were made from two ground stations, Domberg (5,081·6 ft.) and Lelatema (5,323.1 ft.) and from a point called Kibo near Kaiser Wilhelm Spitze which is regarded as the highest point on the crater rim. It was originally intended to include a third ground station, Kifaru, but it was discovered that the ice cap obstructed observations between this point and the top.     

Mixed Integer-Real Valued Adjustment (IRA) Problems: GPS Initial Cycle Ambiguity Resolution by Means of the LLL Algorithm

In order to achieve to GPS solutions of first-order accuracy and integrity, carrier phase observations as well as pseudorange observations have to be adjusted with respect to a linear/linearized model. Here the problem of mixed integer-real valued parameter adjustment (IRA) is met. Indeed, integer cycle ambiguity unknowns have to be estimated and tested. At first we review the three concepts to deal with IRA: (i) DDD or triple difference observations are produced by a properly chosen difference operator and choice of basis, namely being free of integer-valued unknowns (ii) The real-valued unknown parameters are eliminated by a Gauss elimination step while the remaining integer-valued unknown parameters (initial cycle ambiguities) are determined by Quadratic Programming and (iii) a RA substitute model is firstly implemented (real-valued estimates of initial cycle ambiguities) and secondly a minimum distance map is designed which operates on the real-valued approximation of integers with respect to the integer data in a lattice. This is the place where the integer Gram-Schmidt orthogonalization by means of the LLL algorithm (modified LLL algorithm) is applied being illustrated by four examples. In particular, we prove that in general it is impossible to transform an oblique base of a lattice to an orthogonal base by Gram-Schmidt orthogonalization where its matrix enties are integer. The volume preserving Gram-Schmidt orthogonalization operator constraint to integer entries produces “almost orthogonal” bases which, in turn, can be used to produce the integer-valued unknown parameters (initial cycle ambiguities) from the LLL algorithm (modified LLL algorithm). Systematic errors generated by “almost orthogonal” lattice bases are quantified by A. K. Lenstra et al. (1982) as well as M. Pohst (1987). The solution point of Integer Least Squares generated by the LLL algorithm is = (L')⁻¹[L'◯] ∈ ℤ ^m where L is the lower triangular Gram-Schmidt matrix rounded to nearest integers, [L], and = [L'◯] are the nearest integers of L'◯, ◯ being the real valued approximation of z ∈ ℤ ^m , the m-dimensional lattice space Λ. Indeed due to “almost orthogonality” of the integer Gram-Schmidt procedure, the solution point is only suboptimal, only close to “least squares.” ? 2000 John Wiley & Sons, Inc.     

TRIPLE RESECTION: AN EXAMPLE

Abstract

By triple resection is meant the simultaneous fixing of three field points by observations therefrom to two or more points of control. Of several cases one is considered here.     

A TEST FOR THE RELIABILITY OF FIRST-ORDER TRIGONOMETRICAL OBSERVATIONS

Abstract

Generally speaking there is a tendency for observations to be judeged by the magnitudes of the triangular errors, although the misclosures of the side equations are equally important. This note explains how to formulate a compehensive criterion covering the two types of misclosure and given in terms of the mean traingular ? _m for which definite limits are usually laid down.     

THE HEIGHT DETERMINATION OF MOUNT KILIMANJARO TANGANYIKA,EAST AFRICA

Abstract

The following account of the expedition which succeeded in fixing a new height for Mount Kilimanjaro is taken in the main from the diary of the party that made the necessary observations, but, for the sake of clarity, it is as well to set out here a very brief statement of the position.     

A new device for solar observations

Summary After a review of the main causes of the relative inaccuracy of solar observations as compared with star observations, a new device—a “solar prism attachment” to be fitted over the objective of a normal theodolite—for increasing the accuracy and facilitating the observations is described. The results of several practical observations are discussed.     

THE STRAIGHT POSITION LINE

Abstract

The article “Notes on the Position Line” by B. Chiat (E.S.R., xiii, 97, 137) is very informative in the conclusions reached regarding the validity of drawing the position line straight, but it seems, to me at least, that the discussion involving the effects of the earth's non-sphericity is an academic labouring of a difficulty which, in fact, is non-existent.     

Integrating VGI and 2D hydraulic models into a data assimilation framework for real time flood forecasting and mapping

ABSTRACT

Crowdsourced data can effectively observe environmental and urban ecosystem processes. The use of data produced by untrained people into flood forecasting models may effectively allow Early Warning Systems (EWS) to better perform while support decision-making to reduce the fatalities and economic losses due to inundation hazard. In this work, we develop a Data Assimilation (DA) method integrating Volunteered Geographic Information (VGI) and a 2D hydraulic model and we test its performances. The proposed framework seeks to extend the capabilities and performances of standard DA works, based on the use of traditional in situ sensors, by assimilating VGI while managing and taking into account the uncertainties related to the quality, and the location and timing of the entire set of observational data. The November 2012 flood in the Italian Tiber River basin was selected as the case study. Results show improvements of the model in terms of uncertainty with a significant persistence of the model updating after the integration of the VGI, even in the case of use of few-selected observations gathered from social media. This will encourage further research in the use of VGI for EWS considering the exponential increase of quality and quantity of smartphone and social media user worldwide.