## 3 Data-Collection Platforms and Instruments
### Sensor Deployment and Operation over Vegetation Canopies: A Basic Procedural Philosophy  
In the case of vegetation, reflectance is a quantitative measure of color, and it is the main source of information about crop biophysical characteristics. Thus, our primary sensor configuration for measuring reflectance at canopy level is a dual fiber-optic system, with two inter-calibrated Ocean Optics USB2000 radiometers (Dunedin, FL) that collect data from 350 nm to 1000 nm with a spectral resolution of about 1.5 nm. Radiometer #1, equipped with a 25\({}^{\circ}\) field-of-view optical fiber is pointed downward to measure the radiance upwelling from targets, such as a crop. Radiometer #2, equipped with an optical fiber and cosine diffuser (yielding a hemispherical field of view), is pointed upward to simultaneously measure incident irradiance. Therefore, we are not limited to working under clear skies but can collect data under marginal or rapidly changing illumination conditions. The details of our field procedure are summarized by [PERSON] _et al_. [PERSON] et al. (2010) and [PERSON] and [PERSON] (2010). A downward-looking digital camera is typically deployed to document areas scanned by the Ocean Optics sensor and also to facilitate calculation of green vegetative fraction (VF), which is retrieved from the images using the \"excess-green technique\" [PERSON] et al. (2010). Details of the procedure as it relates to our particular system are described in [PERSON] _et al_. [PERSON] et al. (2012), and examples of photos are provided as Figure 1.  
The dual-fiber-optic spectrometer system is deployed over vegetation canopies in two primary ways: (1) by individual field researchers carrying the equipment components from place to place and pointing the sensor at targets of interest; and (2) by researchers operating a tractor equipped with a boom system which allows precise positioning of sensors over the canopies under investigation. Acquiring Spectral-Reflectance Data at Canopy and Plant Community Levels: The Human-Transported Backpack Sensor System  
In our field configuration, depicted as the block diagram in Figure 2, all of the elements, except for the computer, are mounted in a self-contained backpack which includes: (1) an inexpensive WiFi router for the computer connection; (2) a serial terminal server to convert the radiometer serial connection to a TCP/IP network connection; (3) a 12-volt, gel-cell battery; and (4) a voltage converter to provide power to the radiometers. The serial terminal server is the key to separating the instruments from the computer. This device converts RS-232 serial connections to TCP/IP network connections. Driver software on the computer makes this remote connection appear as a local \"com port\" to application software. Two Ocean Optics 2000 hyperspectral field radiometers (as described above) are mounted on the sensor pole along with the light-collecting fibers. In its original configuration, the serial ports on the Ocean Optics systems are interconnected to the backpack using two RS-232 serial cables. In current versions, the Ocean Optics USB interfaces are connected to a USB terminal server. As can be seen in Figure 3, there are several distinct advantages to the configuration. The architecture protects the collection fibers since they are attached only to the pole and to the pole-mounted radiometers. The use of a wireless router means that the computer can be conveniently located within a 300-meter radius from the sensor pole. Because all of the equipment is integrated onto the pole and into the backpack, there are only three connectors (two serial and one power) that need to be attached during equipment setup. Note that excess fiber is coiled and attached to the mounting pole. The amount of excess fiber does not affect the quality of the data taken and facilitates using different mounting configurations when needed.