Owen Wu

	BaySpec’s OCI™-UAV hyperspectral imagers are ultra-compact, easily deployable, high-performance hyperspectral cameras designed specifically for use on small unmanned aerial vehicles (UAVs), to monitor the details of spatial, temporal, and spectral representation of ground objects. It is available in both push-broom and snapshot versions. These cameras cover VNIR wavelength range (custom range available upon request), which is sufficient for varieties of aerial spectroscopic imaging applications such as vegetation characteristics (for example, precision agriculture). Spectral sensing, once integrated on low-cost UAVs, rapidly accelerates application areas such as automatic ground surveys, vegetation development stages studies, and more. 

	Traditionally, widespread adoption of hyperspectral imaging by various industries has been limited due to the lack of fast, compact, reliable, and cost-effective model imagers. To enable the transfer of applications from the lab to industry, BaySpec has overcome the hurdles to miniaturize the instrument in a handheld form. The result is a fully self-contained, highly reliable unit incorporating a hyperspectral image sensor, on-board computer, and battery weighing less than one pound in a volume not much larger than a modern cellular phone. Currently, BaySpec packages a multi-motor UAV platform consisting of an autopilot and an active vibration-isolation gimbal system for its hyperspectral imagers (Figure 1).

	OCI™-UAV-1000 push-broom imagers produce high resolution hyperspectral measurements, up to 100 bands and up to 1 cm ground resolution (Figure 2).

	The real power of hyperspectral imaging is that the continuous and wide-range spectra from each pixel can be used to characterize the materials quantitatively with high accuracy. The abundance of spectral information enables maximum analytical power and automatic chemometrics algorithms to segment the images according to their material characteristics. These spectral signatures enable identification of the materials for quantitative applications, such as forensic analysis, precision agriculture (Figure 3), food processing, biomedical, mineralogy, surveillance, astronomy, and environment analysis, to name a few.

	BaySpec, Inc.
	1101 McKay Drive, San Jose, CA 95131
	tel. (408) 512-5928, fax (408) 512-5929 
	Website: www.bayspec.com

Articles

BaySpec’s OCI-UAV hyperspectral imagers are ultra-compact, easily deployable, high-performance hyperspectral cameras designed specifically for use on small unmanned aerial vehicles (UAVs), to monitor the details of spatial, temporal, and spectral representation of ground objects.

Aerial Hyperspectral Imaging  by BaySpec OCI Hyperspectral Imagers

Early detection of oil conditions can reduce equipment down-time from equipment repairs and allows for optimization of maintenance interval to the lubricant’s ability to protect the equipment. A unique dual NIR and Raman system is utilized for optimized results.

NIR/Raman Oil Condition Monitoring

Biological tissues and other materials often autofluoresce at near-infrared wavelengths, prohibiting Raman acquisition. New, dispersive Raman systems at 1064 nm allow fluorescence-free measurement in similar integration times.

Fluorescence is much more likely and intense at short wavelengths where energies are more apt to cause an electronic transition. Yet even at near-IR wavelengths like 785 or 830 nm, many substances still fluoresce, sometimes prohibiting Raman spectral acquisition. For those users who require longer wavelengths such as 1064 nm, the only available option has been FT-Raman, which is typically noisier and slower than dispersive  Raman systems. But now, BaySpec's new dispersive 1064 nm Raman spectrometer family of instruments offers a turn-key solution that combines the speed, sensitivity, and rugged design of traditional dispersive Raman instruments with the fluorescence avoidance of traditional FT-Raman instruments. 

A variety of animal tissues obtained from a local market were interrogated using two BaySpec benchtop systems: the RamSpec™ 785 and the RamSpec™ 1064. Both systems utilized filtered fiber probes designed for each respective wavelength. Acquisition times were 30 s for both systems. Power was set at 50 mW for the 785 nm measurements, and 150 mW for the 1064 nm measurements. 

Pigmented and porphyrin-rich tissues such as kidney are often too fluorescent to be measured, even at 785 nm; see Figure 1. But using 1064 nm, a clear Raman spectrum relatively devoid of fluorescence background is generated using the same integration time. Additionally, because of the extended quantum efficiency of the InGaAs detector, high wavenumber features (C–H, O–H, and N–H stretching modes) are also simultaneously captured with the same laser.  

Figure 1: Kidney (porcine) is highly fluorescent at 785 nm, preventing extraction of a usable Raman signal. At 1064 nm, however, this fluorescence interference is largely avoided and clear Raman bands are evident. 			

In addition to allowing users the ability to measure Raman spectra from highly fluorescent samples, the dispersive 1064 nm Raman systems also reduce the stringent sampling conditions necessary at shorter wavelengths. For example, 785-nm Raman measurement through vials, cuvettes, or under cover slips often requires that these materials be made of fused silica, quartz, or calcium fluoride for their reduced fluorescence, all of which cost considerably more than bulk glass materials. However, even inexpensive glass sample vials can be used for 1064-nm measurement of weak Raman scatterers such as tissue, owing to the fluorescence avoidance of the longer wavelength approach. 

One of the lingering concerns about the use of 1064-nm Raman is the reduced Raman scattering cross-section. As compared to 785-nm Raman, this cross-section, indeed, reduces approximately 3.4×. However, according to permissible standards for human tissue (skin) exposure, the maximum power level that can be tolerated at 1064 nm is approximately 3.4× higher than the power permissible at 785 nm (1). So, even in photosensitive samples such as biological tissue, the physical reduction in Raman efficiency can be totally compensated by increased laser power.  

Based on these experiments, 1064-nm dispersive Raman will provide a viable new option for those users who are studying highly fluorescent tissues, desire to measure multiple samples in simple glass containers, or those users who are interested in simultaneous fingerprint and high wavenumber spectral acquisition. Future studies will certainly evidence further advantages of this approach, as compared to shorter wavelength (785 or 830 nm) Raman approaches or FT-Raman systems. 

(1) National Institute of Standards and Technology, Z136.1, 76–77, (2007). 

tel. (408) 512-5928, fax: (408) 512-5929  

Owen Wu

Articles

Aerial Hyperspectral Imaging by BaySpec OCI Hyperspectral Imagers

NIR/Raman Oil Condition Monitoring

Tissue Raman Measurement at 1064 nm