Abstract. Systems have been developed and deployed at a North Michigan forested site to measure ambient HONO and vertical HONO flux. The modified HONO measurement technique is based on aqueous scrubbing of HONO using a coil sampler, followed by azo dye derivatization and detection using a long-path absorption photometer (LPAP). A Na 2 CO 3 -coated denuder is used to generate "zero HONO" air for background correction. The lower detection limit of the method, defined by 3 times of the standard deviation of the signal, is 1 pptv for 1-min averages, with an overall uncertainty of ± (1 + 0.05 [HONO]) pptv. The HONO flux measurement technique has been developed based on the relaxed eddy accumulation approach, deploying a 3-D sonic anemometer and two HONO measurement systems. The overall uncertainty is estimated to be within ± (8 × 10 −8 + 0.15 F HONO ) mol m −2 h −1 , with a 20-min averaged data point per 30 min. Ambient HONO and vertical HONO flux were measured simultaneously at the PROPHET site from 17 July to 7 August 2008. The forest canopy was found to be a net HONO source, with a mean upward flux of 0.37 × 10 −6 moles m −2 h −1 . The HONO flux reached a maximal mean of ∼ 0.7 × 10 −6 moles m −2 h −1 around solar noon, contributing a major fraction to the HONO source strength required to sustain the observed ambient concentration of ∼ 70 pptv. There were no significant correlations between [NO x ] and daytime HONO flux and between J NO 2 × [NO 2 ] and HONO flux, suggesting that NO x was not an important precursor responsible for HONO daytime production on the forest canopy surface in this low-NO x rural environment. Evidence supports the hypothesis that photolysis of HNO 3 deposited on the forest canopy surface is a major daytime HONO source.

We present a novel surface reconstruction algorithm which can directly reconstruct surfaces with different levels of smoothness in one framework from height fields using 3D discrete grid ray tracing. Our algorithm exploits the 2.5D nature of the elevation data and the regularity of the rectangular grid from which the height field surface is sampled. Based on this reconstruction method, we also develop a hybrid rendering method which has the features of both rasterization and ray tracing. This hybrid method is designed to take advantage of GPUs newly available flexibility and processing power.

With the advent of high‐powered, commodity volume visualization hardware comes a new challenge: effectively harnessing the visualization power to enable greater understanding of data through dynamic interaction. We examine Cube‐4/VolumePro as the latest advance in real‐time volume visualization hardware. We describe tools to utilize this hardware including a software developers' kit, called the Cube Toolkit (CTK). We show how the CTK supports algorithms such as perspective rendering, overlapping volumes, and geometry mixing within volumes. We examine a case study of a virtual colonoscopy application developed using the CTK.© 2000 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 11, 44–52, 2000

We present an efficient stereoscopic rendering algorithm supporting interactive navigation through large-scale 3D voxel-based environments. In this algorithm, most of the pixel values of the right image are derived from the left image by a fast 3D warping based on a specific stereoscopic projection geometry. An accelerated volumetric ray casting then fills the remaining gaps in the warped right image. Our algorithm has been parallelized on a multiprocessor by employing effective task partitioning schemes and achieved a high cache coherency and load balancing. We also extend our stereoscopic rendering to include view-dependent shading and transparency effects. We have applied our algorithm in two virtual navigation systems, flythrough over terrain and virtual colonoscopy, and reached interactive stereoscopic rendering rates of more than 10 frames per second on a 16-processor SGI Challenge.