ENEV 281 - Chapter 5 – Measuring Vertical Distances Flashcards

A set of vocabulary flashcards covering the principles, equipment, and procedures for measuring vertical distances in surveying.

Elevation

The vertical distance above a datum such as MSL (Mean Sea Level).

Differential Leveling

A common method used to measure vertical distance and determine elevations by establishing a horizontal line of sight with a level.

Back-sight (BS)

A rod reading taken on a point of known elevation, also referred to as a plus sight ($+S$).

Height of Instrument (HI)

The elevation of the horizontal line of sight through the level, calculated as $HI = Elev_A + BS$.

Foresight (FS)

A rod reading taken on a point of unknown elevation, also called a minus sight ($-S$).

Benchmark (BM)

A secure and permanent point of known elevation used as a reference point in leveling surveys.

Turning Point (TP)

A convenient and temporary point used to carry a line of levels forward between benchmarks by using a pair of $BS$ and $FS$ readings.

Running Levels

A process of determining the elevations of several points over a long distance through repeated cycles of differential leveling.

Parallax

An effect to be eliminated by focusing until there is no movement between the reticle and the sighted object in the telescopic sight.

Automatic Level

A type of leveling instrument that depends on gravity acting on an internal pendulum compensator to maintain a level line of sight.

Digital Level

An instrument equipped with a CCD camera that reads a bar-coded level rod to determine elevations.

Level Rod

A rod made of fiberglass or seasoned hardwood with a graduated scale used to take readings through the telescope of a level.

Waving the Rod

A procedure where the rod person moves the rod back and forth toward the instrument to ensure the lowest (most vertical) reading is observed.

Two Peg Test

A field test performed once per day to determine the systematic error of a level by comparing elevation differences from two different setups.

Reciprocal Leveling

A procedure used to cancel or average out instrument errors when measuring across obstacles like rivers where $BS$ and $FS$ distances cannot be kept equal.

Vertical Control Survey

A survey that establishes a series of fixed reference points with a high degree of accuracy to serve as a basis for other surveys.

Error of Closure

The difference between a measured final benchmark elevation and its given known elevation, calculated as $Known - Observed$.

Relative Accuracy

A check on precision expressed as $1:\frac{D}{C}$, where $D$ is the horizontal distance covered and $C$ is the error of closure.

Arithmetic Check

A verification step performed by summing the $BS$ and $FS$ values and applying them to the starting elevation to check for mistakes in field notes.

Level Circuit

A leveling survey that closes back to the starting benchmark or another point of known elevation to ensure no blunders were made.

Precise Leveling

High-accuracy leveling that requires specialized instruments, rods, and procedures such as three-wire leveling.

Correction (for Error Adjustment)

A value calculated as $Error \times \frac{Distance}{Total Length}$ to distribute closing error among measurements in a circuit.

Adjusted Elevation

The final elevation of a point after applying the correction to the observed elevation: $Observed + Correction$.

Systematic Instrumental Error

An error where the line of sight is not horizontal when the bubble is centered; it is canceled if $BS$ and $FS$ distances are kept equal.

Profile

A drawing that shows a vertical section or side view of the earth’s surface along a designed route.

Profile Leveling

The process of determining the elevations of a series of points at uniform intervals along a continuous line, identified by stations and pluses.

Rod Shot

Additional foresight readings taken from a single instrument position during profile leveling to determine ground elevations.

Cross-Section Leveling

Leveling performed on a short line perpendicular to a route centerline to show ground elevations to the left and right.

Trigonometric Leveling

An indirect method of determining elevation differences by measuring a vertical or zenith angle and the horizontal or slope distance.

Station

A point along a continuous line in profile leveling, typically placed at uniform intervals.