Chandler, Jim 
  
associated with carrying out fieldwork are eaed, topography is traditionally measured using manual point gauges, 
which again leads to difficulties in achieving appropriate data densities. 
Techrologicd advances have enabled faster and hence higher resolution data aquisition methods to be used and 
developed. The recat computerization and automation of point gauges (Wallingford, 1999) has enabled individual 
cross ædions to be measured more efficiently in a flume. The time required for ead measurement paint is dill high 
and so measuring reped parallel profiles to provide adigital elevation model (DEM) is an exceptionally slow process 
Laser based instrumentation has offered pdential for flume work also, with gantry mounted laser profilers being 
capable of deriving very dense DEMs. However, the time required for such measurement remains long also and 
problems of defining a stable reference plane suggest that this approad is only pradicable within small areas (« 0.1m). 
For natural field channels, developments in conventional surveying equipment are significant, particularly the 
motorized prism tracking Total Station. This technology has enabled the number of points that can be measured per day 
to be doubled (approximately 2-3000 pánts), and on seaure sites provides a 5096 reduction in personnel. The Total 
Station can certainly provide data a the channel scde and in all diredions, but the density of points is only just able to 
provide information at the bed scde and is certainly incapable of providing anything at the more dusive grain scde. 
2 APHOTOGRAMM ETRIC SOLUTION 
A photogrammetric method d deriving appropriate data for fluvial reseach would appea to dfer potential, and indeed 
photogrammetric methods have been used in earlier studies. Lo and Wong (1973 used 35mm cameras to examine the 
development of rills and gullies on a small sedion of wedahered granite in Hong Kong. Collins and Moon (1979 
measured stream bank erosion photogrammetricdly and this was developed by Welch and Jordan (1983) where non 
metric 35mm imagery was used to meæure œoss ædional profiles and 3D terrain models to represent change occurring 
in a dynamic meander bed. More recently, Lane et al. (1 994) combined analyticd photogrammetry with tacheometric 
methods to quantify change occurring in a rapidly evolving braided pro-gladal channel inthe Alps. A Wild P32 camera 
was used to aauire highly-oblique terrestrial images and this gudy demonstrated just how improved topographic 
monitoring could assst fluvial research, (Lane et al., 1996). 
These studies were dependent upon traditional photogrammetric methods, required acces to expensive 
analogue/analyticd plotters and relied upon manual measurement methods. Developments in digital photogrammetry 
have provided fresh impetus to the use of photogrammetry in fluvial reseach. There ae many major advantages with a 
purely digital solution, particularly if a high-resolution digital camera is included. The equipment necessary for image 
measurement is becoming progressively less expensive, particularly with increasing use of PC platforms. The costs of 
high-resolution digital cameras remain high, but are deceæing (Ahmad and Chandler, 1999) and the spatial acaracy 
adievable is impressive, (Fraser, 1997, Shortis & al., 1998). Competition in the photogrammetric software market is 
intense dso, with prices reducing and capabiliti es increasing. Of significanceto fluvial researchers is the trend towards 
software which demystifies photogrammetry, encouraging ron-photogrammetrists to apply the techniques, (Chandler, 
1999). Most sigrificantly, the software is capable of extrading very dense digital elevation models automaticdly and at 
very high rates. This means that DEMs can be derived at spatial and temporal frequencies that are far more appropriate 
to understanding the fluvial processes eff ecting change. 
Water worked surfaces are ided for automated photogrammetric measurement. The lack of vegetation and natural 
texture ensures that the surfacemeæured coincides with the desired surface urlike automatic terrain measurement for 
conventional urban mapping where vegetation and buildings crede undesirable atifacts. The DEM acquisition 
procedure itself is also enhanced by obtaining imagery using a digital camera, which has a higher dynamic range and 
improved contrast when compared to an analogue image and scanning solution, (Graham, 1998. Image contrast is also 
maximized through the short camera to oljed distances used, which minimizes image degradation due to atmospheric 
haze Finally, the digital camera provides the obvious advantage of instant appraisal of exposures and cf course removes 
thetime consuming and expensive film processing and scanning phases. 
These aombined advantages, reinforced by work in related fields (e.g. Hel ming et al., 1992 Gruen, 1994 Brunsden and 
Chandler, 1996 convinced the authors that a stream bed measurement system based upon digital photogrammetry and a 
high-resolution digital camera was an appropriate technology to invest in and develop. Reseach grant funding enabled 
the purchase of a Kodak DCS460 and DCS420 and purchase and maintenance of the Erdas I magi ne/OrthoM AX and 
OrthoBASE software packages. This combination has subsequently bee used upon a diverse range of fluvial projeds, 
bath in terms of scde, location and desired cutcomes. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 251