## 2. Natural

### a. Climate

#### (1) Description

Weather can have various detrimental effects on leveling accuracy:

• Heat waves are atmospheric anomalies that can randomly bend the LoS or make the rod difficult to read.
• Wind gusts will cause the compensator to bounce as well as make it a challenge to hold an extended level rod vertical.
• A large temperature difference between equipment storage and use requires acclimation time or tripod leg locks may loosen and slip.
• Cold uncomfortable temperatures can result in haphazard work.

#### (2) Behavior

Cumulative effect is random.

#### (3) Compensation

In as much as possible select times and locations minimizing climate impacts. Allow equipment temperature acclimation. Dress for conditions.

### b. Curvature

#### (1) Description

Recall that a level line is curved and the LoS is horizontal. Both coincide at the instrument but separate as the distance from the instrument increases.

#### (2) Behavior

Figure D-11 shows that curvature causes the rod reading to be too high. Figure D-11Curvature Error

The effect of curvature is systematic; it is a function of distance, Equation D-1.

 c = -0.667M2 = -0.0239F2 Equation D-1 c: reading correction, ft M: distance to rod, miles F: distance to rod, 1000s of ft

Note: F in 1000s of feet means, for example, that at 100 ft, F = 100/1000 = 0.1

#### (3) Compensation

(a) Mathematical - Curvature can be accounted for by computing and applying the correction, Equation D-1, to the rod reading.

(b) Procedural - Because curvature is a function of distance, balancing BS and FS distances, Figure D-12, allow it to cancel: CBS (added) is the same as CFS (subtracted). Figure D-12Curvature Compensation

### c. Refraction

#### (1) Description

Even if there are no atmospheric anomalies, the fact that the LoS has to pass through atmosphere causes it to bend, introducing a reading error.

#### (2) Behavior

Refraction causes the LoS to be bent downward, Figure D-13, resulting in a rod reading that is too low. Figure D-13Refraction Error

The effect of refraction is systematic and is a function of distance, Equation D-2.

 R = +0.093M2 = +0.0033F2 Equation D-2 R: reading correction, ft M: distance to rod, miles F: distance to rod, 1000s of ft

#### (3) Compensation

(a) Mathematical - Refraction can be accounted for by computing and applying the correction, Equation D-2, to the rod reading.

(b) Procedural - Being a function of distance, balancing BS and FS distances allows refraction to cancel, Figure D-14: RBS (added) is the same as RFS (subtracted). Figure D-14Refraction Compensation