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1.
《测量评论》2013,45(2):50-57
Abstract

Township plans in Nigeria are, in general, required for the following objects:- <list list-type="alpha"> <list-item>

illustration of existing detail for administrative and other purposes;</list-item> <list-item>

record of property boundaries;</list-item> <list-item>

settlement of property boundaries and registration of title;</list-item> <list-item>

lay-outs and engineering purposes.</list-item> </list>  相似文献   

2.
《测量评论》2013,45(2):71-76
Abstract

In chapter 5, page 12, of my “Report on a Rapid Geological Survey of the Gambia” (Gold Coast Geological Survey Bulletin, NO. 3) I have stated the opinion of Prof. Julius Hann of Vienna that the barometric curves may be analysed into two components:- <list list-type="alpha"> <list-item>

semi-diurnal, constant, depending on latitude and altitude (with a slight yearly alteration);</list-item> <list-item>

diurnal, depending chiefly on temperature (and humidity ?).</list-item> </list>  相似文献   

3.
《测量评论》2013,45(38):466-480
Abstract

Special precautions are taken in the workshop to ensure that divided circles are so mounted that the point from which the circle graduations radiate lies accurately on the axis about which rotation of the circle and reading index or indices takes place. If, through some accident, eccentricity is present, it is still possible to obtain accurate readings if the instrument is used to the best advantage, and the object of the following notes is to assist the surveyor to this end. It will be found that errors arising from eccentricity can be made to cancel out, except in the case of a vertical circle fitted with a single reading index.  相似文献   

4.
《测量评论》2013,45(66):174-176
Abstract

It has been shown in an earlier number of the Empire Survey Review (iv, 24, 70) that if an observer whose eye is at sea level in a calm sea sees an object at a distance s, so that it appears to be on the horizon, then the height of that object above sea level is given by <mml:math><mml:mrow><mml:mi>h</mml:mi><mml:mo>=</mml:mo><mml:mi>K</mml:mi><mml:msup><mml:mi>s</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math> where <mml:math><mml:mrow><mml:mi>K</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mrow><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac><mml:mo>?</mml:mo><mml:mi>k</mml:mi></mml:mrow><mml:mi>r</mml:mi></mml:mfrac></mml:mrow></mml:math>; being the coefficient of refraction and r the mean radius of the earth.  相似文献   

5.
《测量评论》2013,45(30):480-481
Abstract

The condition which must be satisfied for conformal projection from the spheroid to the plane is that <mml:math display='block'><mml:mrow><mml:mi>x</mml:mi><mml:mo>+</mml:mo><mml:mi>i</mml:mi><mml:mi>y</mml:mi><mml:mo>=</mml:mo><mml:mi>f</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mi>ψ</mml:mi><mml:mo>+</mml:mo><mml:mi>i</mml:mi><mml:mi>ω</mml:mi></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mo>,</mml:mo><mml:mtext> </mml:mtext><mml:mo>…</mml:mo><mml:mtext> </mml:mtext><mml:mo>…</mml:mo><mml:mtext> </mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mtext>1</mml:mtext><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> where x and y are the map coordinates; f is any function; ω the longitude; Ψ a variable which is a function of the latitude only; and i = √(?-1).  相似文献   

6.
none 《测量评论》2013,45(51):211-221
Abstract

Formation of Differential Equation.—We now go back to the differential equation given by (9) and substitute in it the values for dw and sin Φ ? sin Φ0 given by (12) and (21), but inserting <mml:math><mml:mrow><mml:mfrac><mml:mrow><mml:msub><mml:mi>V</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow><mml:mi>c</mml:mi></mml:mfrac></mml:mrow></mml:math> for <mml:math><mml:mrow><mml:mfrac><mml:mn>1</mml:mn><mml:mrow><mml:msub><mml:mi>v</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:mrow></mml:mfrac></mml:mrow></mml:math> in (12) and neglecting all terms in the product containing powers of <mml:math><mml:mrow><mml:mfrac><mml:mn>1</mml:mn><mml:mi>c</mml:mi></mml:mfrac></mml:mrow></mml:math> greater than the fourth.  相似文献   

7.
A small area of a mirror can be made vertical with a high degree of accuracy by using a free mercury surface and an autocollimation target made of a mirror. The direction of the horizontal axis of a theodolite can be established, made and kept perpendicular to the vertical mirror for all telescope altitudes and the direction of the line of sight can be made, perpendicular to the horizontal axis with the same high degree of accuracy. Observations can thus be made on any part of a chosen celestial vertical circle much more accurately than by using the best striding levels. This application is potentially useful in determination of: astronomical longitude; changes in longitude differences with time, or the possible East-West component of continental drift; right ascension differences between stars; and the rotation rate of the Earth. Other applications include a leveling instrument of a new type, checking of tubular spirit levels, monitoring tidal variations in the direction of the plumb line, establishing an accurate 90° angle, and checking the graduations of the horizontal and vertical circles of theodolites. The impersonal micrometer for special astronomical observations stops the star image. Only parallel rays will enter the telescope when the observer is tracking the star keeping the star image stationary at the center of cross hairs.  相似文献   

8.
The coefficientsC 21 andS 21 are usually considered to be zero in theory (e.g. the axis of earth rotation was used as the principal axis of inertia). However, satellite measurements show thatC 21 as well asS 21 are non-zero, indicating that the axis of rotation of the earth is not the principal axis of inertia. This work determines the angles by which the principal axes of inertia must be rotated in relation to the geocentric coordinate system (where theZ axis coincides with the rotating axis of the earth).  相似文献   

9.
《测量评论》2013,45(14):502-505
Abstract

For several years it had been realized that aneroids in the Gold Coast showed a distinct lag in the readings when subject to fairly large changes of height. The range of height in the Colony, however, being relatively small and control heights fairly numerous, little interest was taken in the cause, which was generally thought to be due to hysteresis. * All aneroids in use on the Gold Coast are graduated on Airy's scale which is based on latitude 45° and temperature 50° F. In 1921 Mr. C. L. T. Griffith, at that time Chief Instructor of the Survey School, carried out various tests with a number of aneroids, and from these tests concluded that the main source of error arose from inappropriate graduation of the height-scale relative to pressure; using as constants latitude 15°, temperature 86° F., and mean humidity 67 per cent., he worked out a proposed general scale for the Tropics. Ten years later the purchase for test purposes of new aneroids graduated to this scale was considered but was eventually postponed when it was learnt that the question of a special scale for use in the Tropics was under consideration at home by a special Committee consisting of representatives of the Admiralty, War Office, Air Ministry, and National Physical Laboratory.  相似文献   

10.
《测量评论》2013,45(69):322-324
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.  相似文献   

11.
Rotation of the Earth as a Triaxial Rigid Body   总被引：2，自引：6，他引：2  
The Earth is taken as a triaxial rigid body, which rotates freely in the Euclidian space. The starting equations are the Euler dynamic equations, with A smaller than B and B smaller than C. The Euler equations are solved, and the numerical results are provided. In the calculations, the following parameters are used: (C-B)/A=0.003 273 53; (B-A)/C=0.000 021 96; (C-A)/B=0.003 295 49, and the mean angular velocity of the Earth's rotation, ω =0.000 072 921 15 rad/s. Calculations show that, besides the self-rotation of the Earth and the free Euler procession of its rotation, there exists the free nutation: the nutation angle, or the angle between the Earth's momentary rotation axis and the mean axis that periodically change with time. The free nutation is investigated.  相似文献   

12.
One of the important systematic error parameters identified in terrestrial laser scanners is the collimation axis error, which models the non-orthogonality between two instrumental axes. The quality of this parameter determined by self-calibration, as measured by its estimated precision and its correlation with the tertiary rotation angle κ of the scanner exterior orientation, is strongly dependent on instrument architecture. While the quality is generally very high for panoramic-type scanners, it is comparably poor for hybrid-style instruments. Two methods for improving the quality of the collimation axis error in hybrid instrument self-calibration are proposed herein: (1) the inclusion of independent observations of the tertiary rotation angle κ; and (2) the use of a new collimation axis error model. Five real datasets were captured with two different hybrid-style scanners to test each method’s efficacy. While the first method achieves the desired outcome of complete decoupling of the collimation axis error from κ, it is shown that the high correlation is simply transferred to other model variables. The second method achieves partial parameter de-correlation to acceptable levels. Importantly, it does so without any adverse, secondary correlations and is therefore the method recommended for future use. Finally, systematic error model identification has been greatly aided in previous studies by graphical analyses of self-calibration residuals. This paper presents results showing the architecture dependence of this technique, revealing its limitations for hybrid scanners.  相似文献   

13.
精确确定SLR (Satellite Laser Rainging)和VLBI (Very Long Baseline Interferometry) 天线的旋转中心是并址站归心基线测量的关键问题。本文利用两类约束条件建立旋转中心与观测标志之间的直接关系,第1类约束是SLR或VLBI上的观测标志绕其旋转轴旋转形成1个由平面和球面相割得到的平面圆,第2类约束是SLR或VLBI的旋转中心与其垂直轴旋转圆心在同一铅垂线上,与其水平轴旋转圆心在同一水平面上。根据这两类约束条件建立相应的条件方程,利用标志点观测值直接解算旋转中心的坐标及其协方差阵。利用我国2个GNSS (Global Navigation Satellite System) 与SLR或VLBI并址站的实测数据,求解了基于本文直接解法的空间归心基线。结果表明,与已有分步解的差值优于1mm。  相似文献   

14.
Errors are introduced in orthometric height computations by the use of standard formulas to estimate mean gravity along the plumb line. Direct measurements of gravity between the Earth’s surface and sea level from bore hole gravimetry were used to determine the magnitude of these errors. For the seven cases studied, errors in orthometric height, due to the use of the Helmert method for computing mean gravity along the plumb line, were generally small (<2 cm). However, in one instance the error was substantial, being9.6 cm. The results verified the general validity of the Poincaré-Prey approach to estimation of gravity along the plumb line and demonstrated that the suggestion byVanicek (1980) that the air gradient is more appropriate is incorrect. With sufficient topographic information to compute terrain corrections, and density estimates from surface gravity, errors in mean gravity along the plumb line should contribute no more than 3cm to orthometric height computation.  相似文献   

15.
Background

Unlike in the developed countries, Ethiopia does not have carbon inventories and databank to monitor and enhance carbon sequestration potential of different forests. Only small efforts have been made so far to assess the biomass and soil carbon sequestration at micro-level. This study was carried out to obtain sufficient information about the carbon stock potential of Gerba-Dima forest in south-western Ethiopia. A total of 90 sample plots were laid by employing stratified random sampling. Nested plots were used to collect data of the four carbon pools. For trees with a diameter range of 5 cm < diameter < 20 cm, the carbon stock was assessed from a plot size of 49 m2 (7 m * 7 m). For trees with a diameter range of 20 cm < diameter < 50 cm, the carbon stock was assessed from a plot size of 625 m2 (25 m * 25 m). For trees > 50 cm diameter, an additional larger sample of 35 * 35 m2 was used. Litter, herb and soil data were collected from 1 m2 subplot established at the center of each nested plot. To compute the above ground biomass carbon stock of trees and shrubs with DBH > 5 cm, their DBH and height were measured. The biomass carbon assessment of woody species having DBH < 5 cm, litter and herb were conducted by measuring their fresh weight in the field and dry weight in the laboratory.

Results

The mean total carbon stock density of Gerba-Dima forest was found to be 508.9 tons carbon ha−1, out of which 243.8, 45.97, 0.03 and 219.1 tons carbon ha−1 were stored in the above ground biomass, below ground biomass, litter biomass and soil organic carbon, respectively.

Conclusions

The existence of high carbon stock in the study forest shows the potential of the area for climate change mitigation. Thus, all stakeholders at the local and national level should work together to implement effective conservation measures and get benefit from the biocarbon fund.

  相似文献   

16.
Based on the gravity field models EGM96 and EIGEN-GL04C, the Earth＇s time-dependent principal moments of inertia A, B, C are obtained, and the variable rotation of the Earth is determined. Numerical results show that A, B, and C have increasing tendencies; the tilt of the rotation axis increases 2.1×10^ 8 mas/yr; the third component of the rotational angular velocity, ω3 , has a decrease of 1.0×10^ 22 rad/s^2, which is around 23% of the present observed value. Studies show in detail that both 0 and ω3 experience complex fluctuations at various time scales due to the variations of A, B and C.  相似文献   

17.
《测量评论》2013,45(17):138-147
Abstract

While there is no standard method in stadia surveying of taking a set of readings for distance and altitude, the following may be regarded as the conventional, text-book method. The telescope is directed at the staff and the apparent lower hair brought to bear exactly on some convenient foot-mark. The readings of all three hairs are then taken and recorded (4.00, 5.41, and 6·83). Finally the vertical circle is read—to the nearest minute or to a fraction of a minute according to circumstances—and the result entered in the field-book (6° 31′ or 6° 31′ 20″). This method has its merits. It is straightforward and flexible and there is a simple (numerical) check on the accuracy of the staff-readings. Nevertheless it is by no means a perfect method.  相似文献   

18.
《测量评论》2013,45(1):21-24
Abstract

The function of a compass is to indicate the direction of the magnetic field in its neighbourhood. Its pointing is therefore magnetic not geographical. The divergence from a true-north indication, different in different parts of the world, is the “variation” of the compass. This quantity is obviously of importance for true directional work when the magnetic compass is used. Its value is known to a high degree of accuracy and is easily available. Such accurate magnetic data are obtained from an elaborate and special form of compass known as a “Magnetometer” and are regularly published by the Astronomer Royal to an accuracy of about half a minute of arc.  相似文献   

19.
Leaf to canopy upscaling approach affects the estimation of canopy traits   总被引：1，自引：0，他引：1  
In remote sensing applications, leaf traits are often upscaled to canopy level using sunlit leaf samples collected from the upper canopy. The implicit assumption is that the top of canopy foliage material dominates canopy reflectance and the variability in leaf traits across the canopy is very small. However, the effect of different approaches of upscaling leaf traits to canopy level on model performance and estimation accuracy remains poorly understood. This is especially important in short or sparse canopies where foliage material from the lower canopy potentially contributes to the canopy reflectance. The principal aim of this study is to examine the effect of different approaches when upscaling leaf traits to canopy level on model performance and estimation accuracy using spectral measurements (in-situ canopy hyperspectral and simulated Sentinel-2 data) in short woody vegetation. To achieve this, we measured foliar nitrogen (N), leaf mass per area (LMA), foliar chlorophyll and carbon together with leaf area index (LAI) at three vertical canopy layers (lower, middle and upper) along the plant stem in a controlled laboratory environment. We then upscaled the leaf traits to canopy level by multiplying leaf traits by LAI based on different combinations of the three canopy layers. Concurrently, in-situ canopy reflectance was measured using an ASD FieldSpec-3 Pro FR spectrometer, and the canopy traits were related to in-situ spectral measurements using partial least square regression (PLSR). The PLSR models were cross-validated based on repeated k-fold, and the normalized root mean square errors (nRMSEcv) obtained from each upscaling approach were compared using one-way analysis of variance (ANOVA) followed by Tukey’s post hoc test. Results of the study showed that leaf-to-canopy upscaling approaches that consider the contribution of leaf traits from the exposed upper canopy layer together with the shaded middle canopy layer yield significantly (p < 0.05) lower error (nRMSEcv < 0.2 for canopy N, LMA and carbon) as well as high explained variance (R2 > 0.71) for both in-situ hyperspectral and simulated Sentinel-2 data. The widely-used upscaling approach that considers only leaf traits from the upper illuminated canopy layer yielded a relatively high error (nRMSEcv>0.2) and lower explained variance (R2 < 0.71) for canopy N, LMA and carbon. In contrast, canopy chlorophyll upscaled based on leaf samples collected from the upper canopy and total canopy LAI exhibited a more accurate relationship with spectral measurements compared with other upscaling approaches. Results of this study demonstrate that leaf to canopy upscaling approaches have a profound effect on canopy traits estimation for both in-situ hyperspectral measurements and simulated Sentinel-2 data in short woody vegetation. These findings have implications for field sampling protocols of leaf traits measurement as well as upscaling leaf traits to canopy level especially in short and less foliated vegetation where leaves from the lower canopy contribute to the canopy reflectance.  相似文献   

20.
In an elementary approach every geometrical height difference between the staff points of a levelling line should have a corresponding average g value for the determination of potential difference in the Earth’s gravity field. In practice this condition requires as many gravity data as the number of staff points if linear variation of g is assumed between them. Because of the expensive fieldwork, the necessary data should be supplied from different sources. This study proposes an alternative solution, which is proved at a test bed located in the Mecsek Mountains, Southwest Hungary, where a detailed gravity survey, as dense as the staff point density (~1 point/34 m), is available along a 4.3-km-long levelling line. In the first part of the paper the effect of point density of gravity data on the accuracy of potential difference is investigated. The average g value is simply derived from two neighbouring g measurements along the levelling line, which are incrementally decimated in the consecutive turns of processing. The results show that the error of the potential difference between the endpoints of the line exceeds 0.1 mm in terms of length unit if the sampling distance is greater than 2 km. Thereafter, a suitable method for the densification of the decimated g measurements is provided. It is based on forward gravity modelling utilising a high-resolution digital terrain model, the normal gravity and the complete Bouguer anomalies. The test shows that the error is only in the order of 10−3mm even if the sampling distance of g measurements is 4 km. As a component of the error sources of levelling, the ambiguity of the levelled height difference which is the Euclidean distance between the inclined equipotential surfaces is also investigated. Although its effect accumulated along the test line is almost zero, it reaches 0.15 mm in a 1-km-long intermediate section of the line.  相似文献   

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