83 / 353 
too dark, limiting the 
data analysis we have 
route, reported on the 
when moving through 
both sides. This sort of 
ve consequences: from 
'educing the number of 
PDOP value, from the 
f multipath phenomena 
leasurements. The red 
ere the geometry of the 
Route 1: time was lost 
>f satellite geometry. 
te relative accuracy. 
foute 1 
inates of all collected 
em from the WGS-84 
"or this task we used 
ire software developed 
titute of Oceanography 
tble on the Internet. 
>f local transformation 
ering whole Italy. It is 
ransformation partially 
in terms of absolute 
id with the Backpack 
sensor adopted in the 
;itive to nearby ferrous 
leld source. During our 
clearly visible metallic 
objects nor we can exclude that other unrecognized magnetic 
sources could have affected the DMC measurements. However 
we were not able to determine how much this sensor could be 
influenced by such disturbances. 
5. CONCLUSIONS 
In this paper we have presented an application of the Backpack 
MMS to a real case scenario: the mapping of escape pathways 
on a volcanic island for civil defence purposes. Three different 
routes were surveyed collecting images and both positional and 
orientation data. Achieved results showed in most cases that the 
Backpack performed better in terms of relative accuracy than in 
absolute positioning. On the other hand the latter is affected by 
several factors which can be only partially compensated for. 
The test has also shown that this pedestrian system can 
potentially solve the need for detailed surveys on natural risk 
areas where classical van-based MMS cannot operate. However 
several improvements have to be done in terms of portability, 
flexibility and ease of use of the system. For instance the weight 
of the Backpack is of concern: in our case the operators had to 
bring in the rucksack about 10 kg of material, distributed 
between batteries, laptop PC and GPS receiver. A possible 
solution could be to use a pocket PC instead of a laptop, given 
that the computer is needed only for sensor sychronization and 
for the DMC data storage. Moreover power consumption has to 
be considered: using a small 12V/15A recheargable lead battery 
the system could be continously operated for about 2.5 hours, 
after this time we had to stop the system in order to change the 
supply. In total three batteries were needed to survey each route. 
Further improvements can also be made to increase the 
accuracy of position and attitue data. The DMC is one of a 
handful of devices that can provide the attitude of the Backpack 
MMS. However other kind of orientation sensors, less sensitive 
to magnetic disturbances could be investigated. RTK GPS 
would certainly help the operator during survey by indicating 
the current positioning accuracy in real time, alternatively a 
GPS antenna, more effective for multipath rejection, could be 
tested. 
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