518
J. Ojeda Zújar et al.
Detailed Air photographs: we have available four photogrammetric flights, all in
winter, a critical point because of the strong seasonality of the maritime climate in
this zone.
February
1979 1:10000
April
1989 1:5000
December
1994 1:3000
February
1996 1:3000
The geometrically consistent integration of the air photos into the GIS required a
preliminary digital processing by scanner and Desktop Mapping System 4.0 . This
software eliminated tilt and radial distortion (ASPRS, 1996) and allowed the
production of vector format output by stereoplotting (spot height, coastline/foredune
planimetry etc.) or raster mosaics (orthophotos and DTM).
Field Survey: this was carried out with a Leica TC600 infrared Total Station
with a vertical or horizontal angular accuracy of 5" , a distance meter accurate to
3mm ±3ppm and an operating range between 1.1 and 1600m. This equipment was
used to survey the ground control points for air photo rectification and then to
assess the actual working accuracy of the Leica 200 GPS system. All GPS surveys
were made by a mobile rover receiver (Leica 200 GPS) and postprocessed and
differentially corrected (Cook et al., 1996) using data from a master receiver
(Leica 200 GPS) fixed in a known location (bench mark). The operating range
between the two receivers was 10-15 km.. The three available modes were used as
follows:i)static mode: x,y,z accuracy = 5mm ± 1ppm.: measuring time 10-15
minutes: used for measuring ground control points for new air photos
ii) stop-and-go mode: x,y,z accuracy = 3mm ±1ppm: measuring time 15
minutes to start and 25 seconds per new point: used to survey point
heights on the foredune in order to improve DTM quality, the coastline
using the foredune/backshore contact line, and the 1997 landward limit of
foredune propagation
iii) cinematic mode: x,y accuracy = 3cm ±1ppm and z accuracy = 6cm
±1ppm: measuring time is 15 minutes to start then automatic continuous
measurement: used to survey coastline in 1997
Results and Interpretation
Annual foredune retreat rate: each rectified or orthophoto was introduced into
ArcInfo through a compatible format (TIF) and three measurements ( west, centre,
east) were made at each date with the following results:
J. Ojeda Zújar et al.
Detailed Air photographs: we have available four photogrammetric flights, all in
winter, a critical point because of the strong seasonality of the maritime climate in
this zone.
February
1979 1:10000
April
1989 1:5000
December
1994 1:3000
February
1996 1:3000
The geometrically consistent integration of the air photos into the GIS required a
preliminary digital processing by scanner and Desktop Mapping System 4.0 . This
software eliminated tilt and radial distortion (ASPRS, 1996) and allowed the
production of vector format output by stereoplotting (spot height, coastline/foredune
planimetry etc.) or raster mosaics (orthophotos and DTM).
Field Survey: this was carried out with a Leica TC600 infrared Total Station
with a vertical or horizontal angular accuracy of 5" , a distance meter accurate to
3mm ±3ppm and an operating range between 1.1 and 1600m. This equipment was
used to survey the ground control points for air photo rectification and then to
assess the actual working accuracy of the Leica 200 GPS system. All GPS surveys
were made by a mobile rover receiver (Leica 200 GPS) and postprocessed and
differentially corrected (Cook et al., 1996) using data from a master receiver
(Leica 200 GPS) fixed in a known location (bench mark). The operating range
between the two receivers was 10-15 km.. The three available modes were used as
follows:i)static mode: x,y,z accuracy = 5mm ± 1ppm.: measuring time 10-15
minutes: used for measuring ground control points for new air photos
ii) stop-and-go mode: x,y,z accuracy = 3mm ±1ppm: measuring time 15
minutes to start and 25 seconds per new point: used to survey point
heights on the foredune in order to improve DTM quality, the coastline
using the foredune/backshore contact line, and the 1997 landward limit of
foredune propagation
iii) cinematic mode: x,y accuracy = 3cm ±1ppm and z accuracy = 6cm
±1ppm: measuring time is 15 minutes to start then automatic continuous
measurement: used to survey coastline in 1997
Results and Interpretation
Annual foredune retreat rate: each rectified or orthophoto was introduced into
ArcInfo through a compatible format (TIF) and three measurements ( west, centre,
east) were made at each date with the following results: