International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
  
3. ISSUES 
During the past 5 years a number of workshops have been held 
to discuss the developments in LiDAR and IfSAR and from 
these a number of conclusions can be drawn. Table 2 compares 
a number of characteristics of the two data types. 
  
LiDAR 
IfSAR 
  
Operational 
at altitudes from 50m to 3500m. 
Space borne systems also in use. 
Acquired from fixed wing and helicopter platforms, 
Operates in day and night and in moist 
Acquired from aircraft at high altitudes using single 
pass systems and from satellite platforms using 
single and repeat pass systems. 
Operates in all conditions, although atmosphere can 
  
  
  
atmospheres. affect accuracy. 
Image Intensity image available with some sensors. Amplitude image created as part of system from 
Frequently flown with digital camera. SAR. 
Calibration Not fully developed. Well developed and essential. 
Processing XYZ co-ordinates generated directly to form DSM. | Complex processing now using mature algorithms 
for DSM and orthoimage generation. 
Layover and shadow will cause problems from 
once only acquisition, but can be overcome by 
multiple acquisition. 
Coherence not a problem for single pass systems. 
  
Post processing 
Processing packages available. 
Produces DSM which needs processing to DTM. 
Good algorithms exist, but still not fully reliable. 
Produces DSM which need processing to DTM. 
Significant editing still required. 
Response from different types of surface cover not 
fully understood. 
  
Characteristics of 
DSM Footprint size also varies. 
returns. 
Gaps in data due to occlusions. 
Density varies with sensor and altitude. 
Ground and tree surface can be seen with multiple 
Footprint larger than LiDAR, tends to smooth out 
features. 
Some penetration from trees, varies with frequency. 
  
Accessibility to data | Point cloud easily understood. 
Many companies offer data acquisition and 
Complex processing generally done by system 
operator. SAR data not familiar to many people 
and nature of the DEM not always understood. 
  
  
  
  
  
and standards also being developed. 
  
processing. 
Software available for filtering, feature extraction Few operators. 
etc. 
Accuracy Best accuracy around 10cm in Z Best accuracy around 0.5m in Z 
Applications Applications over limited areas with high accuracy. | Suited to larger areas with lower accuracy. 
2 2 
Cost $500 per m^ $5 per m* 
Standards LAS standard developed in USA. Specification Reliant on system operator. 
  
  
  
Table 2. Comparison of airborne LiDAR and IfSAR. 
4. PROCESSING AND CALIBRATION 
Calibration of LiDAR data by the user is not well developed. 
Normally a calibration surface will be measured prior to a flight 
to determine bore sight alignment and any systematic error. A 
datum shift can be applied to the measurements if necessary. 
Some operators do not consider this to be necessary. In fact 
there are many sources of error which are not accounted for. 
Katzenbeisser (2003) has studied these and shows that “most of 
the corrections, which might be applied have to be used at a 
very early stage of the data processing. Even if so called “raw 
data” (i.e. all echo coordinates) are available, the correction is 
limited to GPS (or positioning) errors.” He goes to to write that 
“The usual calibration flights (at the beginning and at the end of 
a survey) over flat terrain do not allow the detection of distance 
errors, of varying deflection errors, of time delays between 
measurements, etc. It seems that it is much more essential to 
understand the composition of a sensor system and what the 
manufacturer has done to avoid most of the effects.” 
Katzenbeisser also suggests that general software for processing 
real raw data (i.e. position, orientation and distance) may never 
exist, as it would have to take into account a large number of 
parameters assigned with the individual manufacturing of a 
sensor system and which can not be generalized. Filin (2003) 
has also investigated correction of systematic errors in LiDAR 
and indicates the need for an error model for LiDAR. 
The processing of the IfSAR data is now well established but 
there are still problems, especially when high accuracy is 
required. The main inherent problems are the presence of 
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