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How to: Some Basic Principles for Leveling - ppt download

How to: Some Basic Principles for Leveling - ppt download

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Lecture Overview Equipment Introduction to Leveling Observation, Field Notes, and Computation Errors and their effects ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov. 2006
Tilo Schöne. GFZ, Germany.
Observation, Field Notes, and Computation. Errors and their effects. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Equipment ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov. 2006
Change plate (German: Frog/Frosch) Pole staff bubble (bull eye) Marker. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Automated Levels. Easy to use (not power!) Needs experience. Robust even in hostile environment. Digital Levels. Push-button technique. No reading errors, special staff. Readings are stored and analyzed digitally. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Pendulum. Bull Eye. Tribrach. Courtesy: Deumlich, Vermessungskunde. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Download to the computer. Automated height computation + adjustment. No feeling for quality anymore. You frequently need power plugs. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
From easy to sit to ops, this is high ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Wood, aluminum. INVAR type for high precision leveling. Barcode. for Digital Levels. Conventional ( E -type) ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
For long survey lines. Allows change of instruments. Best is a metal change plate. Screws e.g. at fences. Sharp stones or nails. Beware of dark colors. It’s not the Indonesian- German Dictionary, It’s the nail! ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Any tilt will disturb your readings. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Should be long-term. Preferable in bedrock, settled buildings, or bridges. Do not use fences or walls. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Level surface (e.g. the geoid) A water surface with no motion. Gravity gradient is the normal to the level surface. The Instrument’s Bubble is in the normal (!) Horizontal surface. At the instruments axis, the horizontal surface is tangent to the level surface. Over short distances (<100 m) the horizontal surface and the level surface will coincide. For long leveling lines the effects of the gravity field must be considered. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Measures height differences between points. Along a line. Several points from one occupation. Leveling rods. Line of sight. Back sight. Fore sight. Gravity Gradient. fs. bs. Dh = bs - fs. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
The first reading from a new instrument stand point (i.e. take the height to the instrument) Fore sight (FS) The last reading from the current instrument station (i.e. give the height to a benchmark) Intermediate sight (IS) Any sighting that is not a back sight or fore sight. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Check yourself for frequent used numbers (2/3) or (7/8) ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Always start and finish a leveling run on a Benchmark (BM or TGBM) and close the loops. Keep fore sight and back sight distances as equal as possible. Keep lines of sight short (normally < 50m) Never read below 0.5m on a staff (refraction) Use stable, well defined change points. Beware of shadowing effects and crossing waters. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
New Benchmark. NB Tidal Hut. TH. S1. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
´ ´ (SOLL – IST) ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
The difference of the measured height difference (DHmeas) to the known height (closed loops = 0, known benchmarks = height difference) Misclosure = DHSOLL – DHIST. Point errors at double observed points. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Roughly from the instrument. NI002 = 0,2mm/km (doubled line) NI025 = 2.5mm/km (doubled line) Survey line length dependent. ms = m1km s, s in km. mH = (m1km/2) s, s in km #(middle of the line) ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Small misclosures in closed level loops are expected because of the accumulation of random errors and can be adjusted. If the misclosure is large, the loop (or part of it) must be repeated. Misclosures can also result from errors in published BM levels and from BM instability. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
For our example, a second order leveling standard is adopted*… misclosure  2,5s mm. where s is the length of the line in km. *Dependent on your contry’s rules and the instrument used. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Acceptable error is. 2.5(0.4) = ±1.6 mm. The misclosure of +1 mm is within the limit. Mean error for NB1 = 2.5/2* (0.4) ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Change point / staff instability. Instrument or Benchmark instability. Refraction. Uncalibrated staff or levels. Reading, booking, or computation errors. Fore- and backsight distances different. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Earth curvature. Refraction. Collimation errors. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Horizontal Level. Curvature effect. (r +Dh)2 = r2 + s2. => Dh  s2/(2r) Distance (s) in m Effect (Dh) in mm. 0,008. 0,03. 0,2. 0, ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Leads to an incorrect staff reading. line of sight. error. horizontal line. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Stand point 1. Stand point 2. a′1 = a1+e. b′1 = b1+2e. Δh = a1−b1. Δh′1 = a′1−b′1 = a1−b1−e = Δh−e. With Δh′1+e = Δh′2−e. Δh′2−Δh′1. 2. a′2 = a2+2e. b′2 = b2+e. Δh = a2−b2. Δh′2 = a′2−b′2 = a2+e−b2 = Δh+e. Δh =Δh′2−e. e = ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Summary ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov. 2006
The bubble tube must be leveled before the reading. Beware of sun exposure (will wander) Ensure the instruments pendulum is in-limit. The instrument must be set up in the middle between two staffs. Prevents curvature effects. If impossible, use the same distances, but opposite for the next readings. You must not use the parallax screw between the backsight and foresight readings. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov
Surface refractions. Beware also of temperature gradients (inside/outside buildings) !!!! Staff should be set up vertically. A change plate should be used. Leveling must be done in two opposite directions but the same line (beware of gravity gradients) Staff should be calibrated, especially if INVAR. Be careful when crossing rivers (large water surfaces) Use same-time (mutual) observations. Repeat it during different times of the day. ODINAFRICA/GLOSS Sea Level Training Course - Oostende, Belgium Nov