In: Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7,2010, IAPRS, Vol. XXXVIII, Part 7B 
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measure incoming radiation and the other one looked 
downward, to measure reflected radiation. This design enabled 
direct estimation of reflectance values for the specified bands as 
ratio of reflected to incoming radiation. 
Both sensor boards were bolted to poly vinyl chloride (PVC) 
endcaps. For the downward looking sensors, a PVC pipe of 
0.23m long with 0.10m diameter was attached to the endcaps, 
creating a 26° field of view (Figure 2). For the upward looking 
sensor boards, a PVC pipe of 0.04m was fitted to generate a 
field of view of 100°. The open or sensing ends of both the 
pipes were closed and sealed with 4mm thick flat Delrin 
(Polyoxymethylene), a polyplastic engineered to facilitate the 
diffusion of electromagnetic radiation and minimization of 
angular reflection effects. 
Downward looking sensor Upward looking sensor 
Figure 2. Structure of sensor board mounting with PVC tubes 
for downward and upward looking sensors. 
Each sensor pair was calibrated using 99% reflectance 
Spectralon (Labsphere, NH, USA) reference panels measured 
with an Analytical Spectral Devices (ASD) FieldSpec® 
spectroradiometer (ASD, Inc., CO, USA). 
2.3 Sensor Integration with Mote 
Data collection, conversion and transmission were achieved 
using MICA2 wireless motes (Crossbow Technology), 
operating at an RF frequency of 433 MHz, interfaced to an 
MDA 300 analogue to digital converter board (Crossbow 
Technology). The motes were programmed with a version of 
Xmesh (Crossbow Technology Inc. 2007; Tiny 2009) software 
(Crossbow Technology) specific for the MDA300 A/D board. 
The standard Xmesh software was modified and customized 
(Dragonnorth Pty Ltd, Needham, MA, USA) to provide control 
of the sensor board used to coordinate the acquisition of 
readings from the seven sensors on two heads through tow data 
acquisition channels. A 6V sealed lead acid battery provided 
power for both the sensor boards and the mote 
The network was routed through a gateway consisting of a 
MICA2 mote connected to a MIB510 serial interface board in 
turn connected to a laptop computer running the Xserve data 
acquisition software (Crossbow Technology). The stored data 
was accessed and the network was managed using the 
MoteView (Crossbow Technology) as the client. 
Broadband connection of the local server to the Internet was 
provided using a CDM882-SEU wireless router (Call Direct, 
Sydney, AU) using the Next G network (Telstra, Melbourne, 
AU). 
2.4 Establishment of Wireless Network 
Establishment of the wireless network and real-time data 
acquisition involved 3 software tiers: 1) Mote layer- sensor 
nodes were connected to form a multi-hopping mesh network 
and a gateway node forwards data messages into and out of the 
mesh, 2. Server layer- facilitated translation and buffering of 
data from the wireless mesh network and forms the bridge 
between the wireless motes and the internet clients, and 3. 
Client layer- provided the user visualization software and 
graphical interface at PC terminal for managing the network. 
JH 
PC TerminaL ,. „ 
/ 
4 Mote Laver f Server Layer Client Layer 
(XMesh, Sensor Apps) (Database, logger) (Visualization, 
Analysis Tools) 
Figure 3. Software and hardware framework for establishment 
of wireless network. 
2.5 Field Installation 
For field (ground) installation, sensors were attached to square 
(width: 3.5mm) base steel poles, such that the sensors were 
positioned circa 2m above the soil surface (Figure 4). This 
configuration created a 0.9m diameter footprint, for the 
download looking sensor with the 26° field of view (FOV), 
allowing 4-5 rows of crop to be sensed. 
Figure 4. Design of wireless sensor field unit. A voltage 
regulator in the battery case provides 3V input 
power to mote box and 6V power to two sensor 
boards through a terminal board in the mote box.