THE USEFULNESS OF MULTICOMPONENT, TIME-DOMAIN AIRBORNE ELECTROMAGNETIC MEASUREMENTS

Time-domain airborne electromagnetic (AEM) systems historically measur e the inline horizontal (x) component. New versions of the electromagn etic systems are designed to collect two additional components [the ve rtical (z) component and the lateral horizontal (y) component] to prov ide greater diagnostic information. In areas where the geology is near horizontal, the z-component response provides greater signal-to-noise , particularly at late delay times. This allows the conductivity to be determined to greater depth. In a layered environment, the symmetry i mplies that the y component will be zero; hence a nonzero y component will indicate a lateral inhomogeneity. The three components can be com bined to give the ''energy envelope'' of the response. Over a vertical plate, the response profile of this envelope has a single positive pe ak and no side lobes. The shape of the energy envelope is dependent on the flight direction, but less so than the shape of the x-component r esponse profile. In the interpretation of discrete conductors, the z-c omponent data can be used to ascertain the dip and depth to the conduc tor using simple rules of thumb. When the profile line is perpendicula r to the strike direction and over the center of the conductor, the y component will be zero; otherwise it appears to be a combination of th e x and z components. The extent of contamination of the y component b y the x and z components can be used to ascertain the strike direction and the lateral offset of the target, respectively. Having the z and y component data increases the total response when the profile line ha s not traversed the target. This increases the possibility of detectin g a target located between adjacent flight lines or beyond a survey bo undary.