ALS

Airborne Laser Survey

 

 

 

 

 

 

 

 

 

 

   Airborne Laser Survey  |  ALS in the Power Facilities | ALS in Oil & Gas Facilities | ALTEXIS Software | FALCON - Lidar Sensor |

 

 

Aeromap Technology Systems (AeroMap) in collaboration with its partners engages in the performance of comprehensive aerial survey of overhead power transmission lines. The technology applied is based on proprietary software and techniques using up-to-date aerial survey and geodetic equipment mounted on fixed wing or rotary aircraft.

 

A data collection subsystem provides for the use of various aerial photogrammetry and remote sensing methods to obtain a maximum volume of data on power transmission lines and their infrastructure within a corridor of up to ±200m wide.  Ground survey methods are also employed to support aerial survey data and, in some exceptional cases, they serve as the main source of survey line data when it is impossible or difficult to obtain data because of adverse GPS conditions, prohibition of flights, etc.  The bulk of data is collected through aerial surveys conducted by specialized flying laboratories.

 

Aerial survey modes:

The required survey parameters are achieved in a single pass of a survey aircraft above the survey line thus reducing the cost of aerial work. As laser scanning is carried out using equipment which is capable of registering both the FIRST and the LAST reflections, scan densities correspond to LAST pulses reflected from the ground and ground objects (above all, buildings and structures). An actual scan density is 30-40 percent higher due to FIRST-pulse reflections which account basically for towers, conductors, strings of insulators and vegetation.

 

Overhead power transmission lines are surveyed with the scanning unit mounted at an angle of 20 degrees in the direction against the flight path. Such a position of the scanning unit does not affect the quality of ground and ground objects surveys allowing to receive reflected pulses and locate vertical structures accurately, including towers (poles in particular), insulator strings, guys, cross arms as well as substation enclosures (fences)

 

Main objectives of digital aerial photography: 

  • Collection of data needed to assess the condition and troubleshoot any faults on power transmission lines;

  • Office interpretation of powerline infrastructure;

  • Use of digital photos to create digital orthophoto maps and outlining the contours of objects on such maps;

  • Stereoscopic analysis of images to ensure a better interpretation and stereophotogrammetric analysis of stereographs with the measurement of horizontal and vertical coordinates of objects.

 

Assessment of condition:

  • Inspection of overhead power transmission lines within the right-of-way of ±50 m from line axis, identification of troubles;

  • Documentation of overhead power transmission lines, measurement of actual line parameters such as span lengths, sags, clearances, etc., identification of deviations from design;

  • Inspection of substations and other power engineering facilities

 

Engineering surveys:

  • Pre-design inspection of overhead power transmission lines for rehabilitation, laying fiber-optic cables, etc

 

Topography, geodesy and land management:

  • Creation of topographic plans on a scale of 1:1000 and smaller;

  • Creation of cadastral plans

 

Power Line Parameters Subject to Aerial Surveying:

High-density scanning (over 10 points per square meter) delivers detailed laser images of all significant elements of power transmission lines and helps determine their exact location and make high-accuracy measurements. In particular, laser scanning survey data can be used to determine types of towers, supports as well as the condition of foundations being surveyed.

 

Guaranteed accuracy of laser scanning survey data:

  • Horizontal geodetic coordinates of towers - 0.2 m;

  • Elevations of towers - 0.5 m;

  • Span lengths; span elevation differences; distances to the ground, vegetation and conductors of crossing power lines - 0.2 m;

  • Sags - 0.2 m;

  • Power line pivot angles - 0.2°;

  • Geographical referencing of orthphoto plans - 0.2 m;

  • Angles of deviation of insulators -5°;

  • Distances to identified geographical objects - 1.0 m

 

The selected method of laser scanning survey and aerial digital photography allows the identification of the following deficiencies on overhead power transmission lines:

 Damages or problems along routes and clearings:

  • Trees and shrubs under conductors growing up to 4 m or higher

  • Individual trees at edges of clearings which threaten to fall on wires of overhead power transmission lines

  • Vegetation growing within a 2m zone around towers

  • Absence or defective condition of tower base protection against ice drift, erosion from runoff of rain and melted snow and wind erosion of sand

  • Absence or defective condition of collision fenders and clearance gates at railway crossings

 

Damaged towers and foundations:

  • Longitudinal or lateral tilt of towers exceeds permitted values; distorted elements of towers; lack of alignment between guyed tower legs and footings

  • Tower foundations or reinforced concrete tower legs are buried to a depth below design specifications

  • Soil subsidence or heaving around foundations, sinking or squeezing of foundations;

  • Distorted elements of towers

  • Foundations are not protected against wind erosion of sand and adverse impact of aggressive water

  • Slackened or damaged tower guys or internal ties in reinforced concrete towers

  • Nests of birds or other foreign objects on towers which may cause outages.

 

Faulty conductors or ground wires:

  • Unbalanced condition of phase conductors

  • Unacceptable changes in sags and distances from conductors to the ground, crossing objects and between phase conductors

  • Loops approaching anchor and angle supports; excessive convolution of loops

 

Damaged suspension insulators and fixtures:

  • Mechanical damages porcelain or glass insulators

  • Defective insulators

  • Unacceptable deviation of suspensions from the design position

  • Damaged protective horns and rings

 

The following parameters can be controlled after surveys of overhead power transmission lines:

 Conductors and wires:

  • Mechanical damages porcelain or glass insulatorsActual sag of conductors and wires must not deviate from design specifications more than ±5% (having regard to ambient temperatures at the time of measurement).

  • Aerial insulation distances between loop conductors and the body of the tower as well as between conductors of overhead power transmission lines at intersections with other conductors when transposed on towers, taps and transitions, must not deviate from design specifications more than minus 10%.

  • Unbalanced condition of various phase conductors in respect to each other as well as that of wires must not be allowed greater than 10% of the design sag of the conductor (wire).

 

Line insulation

  • Acceptable deviation of suspension insulators from the design position along overhead power transmission lines

  • Difference in lengths of strain insulators for conductors of the same phase having a common point of attachment to the cross-arm must not be greater than ±1 % of the insulator length

 

Data Output:  Please see Altexis Software for more data explanation

Aerial survey data are processed using develop in house software package or any other software preferred by end user (Aeromap offer Altexis or  TopPIT) for the comprehensive laser data analysis and, in particular, for the creation of vector models of overhead power transmission lines

 

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