Geophysical Mapping: Method Details
Printer Friendly Version  
6 of 48
Method Name: Airborne spectrometry
Method Type:   Radioactivity
Assigned Problems:
+ Regional Mapping Regional Mapping
   '+' = Technique applicable
Principle:   Airborne spectrometry is a technique that provides information about the distribution of the natural isotopes (e.g., elements Potassium (K), Uranium (U) and Thorium (Th)) as well as of artificial isotopes (e.g., 137Cs).
Keywords:   Airborne spectrometry; airborne radiometric surveys; natural and artifical isotopes; radiometric element concentration; gamma rediation
  • Target must be characterized by sufficient radiometric-element contrast
  • Survey data corrections needed (e.g., flight height; background scattering)
  • Spectrometry should be postponed for about 12 to 24 hours following a 'ground soaking' rain, to allow soil moisture levels to return to 'pre-rain' levels
Resolution:   A single measurement provides an average surface concentration for an area of several thousand square metres, composed of variable proportions of bedrock, overburden, soil moisture, water and vegetation.

Spectrometry measures effects generated within the first 0.3 m of the underground, thus, has almost no penetration depth. However, the overburden bears a relationship to the underlying bedrock in certain environments.

Expected Results:  
  • Measured parameter: counting rate in counts / min or counts / s
  • Data analysis: count rates may be converted to ground concentrations (in [ppm] for Uranium and Thorium; in percent for Potassium [%]) or activities (in Curie per volume (litre) [Ci / l] or Bequerel per volume [Bq / m3]) for Radon. Data is plotted in contour maps
  • Interpretation: requires an understanding of the nature of the surficial materials and their relationship to bedrock geology. The processing and interpretation may require a digital elevation model.
Combination with other Methods:  
  • Required additional information: NA
  • Related add-on information: airborne magnetic data; electromagnetic data
  • Independent additional information: airborne gravimetric data
Operating Expense:  
  • Crew size: flight crew (normally 2 pesons); processing and interpretation: 1 key person
  • Acquisition speed: 30 - 500 km2 per day, dependent on aircraft type, line spacing and instruments
  • Processing: Requires 1 - 2 days per acquisition day
  • Equipment rental costs: high
Parameters to specify:  
  • Flying height (distance from source)
  • Variables to be measured, instruments required (i.e., Integral or spectral measurements)
  • Volume of detector required (i.e. for airborne gamma-ray spectrometry)
  • Direction of flight (usually 'cross-strike')
  • Flight line spacing (between 250 m and 1000 m)
  • Extent of survey
  • Tolerances for altitude and positional deviations
QC Documents:  
  • Calibration information
  • Document applied corrections (e.g., subtraction of background counts)
  • Field notes (e.g., all activities, effective time schedule, present personnel)
  • Maps of total gamma radiation, radiation within a range of interest (ROI), or spectral fractures of the radiation spectrum
  • Maps of radiometric element-concentrations
  • Interpretation
Printer Friendly Version