Sensors & Software Inc. NG250 ユーザーズマニュアル
Noggin
12-Survey & Map Mode
81
12.2.11.2 Identifying Air Reflections
Some hyperbolic reflections can also be caused by objects not in the subsurface such as fences,
overhead wires and, in some conditions, even large trees.
overhead wires and, in some conditions, even large trees.
An important part of data interpretation is learning to recognize these unwanted “air” events and
differentiate them from the desired subsurface events. Good field notes are indispensable for
helping identify unwanted events on the data.
differentiate them from the desired subsurface events. Good field notes are indispensable for
helping identify unwanted events on the data.
One way of identifying air reflections is to use the hyperbola fitting method. If the object is in air,
the radar velocity will be 0.3 m/ns or 0.984 ft/ns and will be much faster than if it is in the ground
(v ~ 0.1 m/ns or 0.328 ft/ns).
the radar velocity will be 0.3 m/ns or 0.984 ft/ns and will be much faster than if it is in the ground
(v ~ 0.1 m/ns or 0.328 ft/ns).
Figure: 12-5 Hyperbola matching can be used to identify reflections from objects that are not in the subsurface but
are from objects above ground. If the hyperbola matching velocity is near the speed of light (0.3 m/ns or 0.984 ft/ns)
then the hyperbola was caused by surface object like a overhead wire, tree, etc. After matching the hyperbola (right),
the “depth” value displayed on the bottom of the screen is really a measure of how far from the survey line the object is.