scholarly journals Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy

2012 ◽  
Vol 12 (17) ◽  
pp. 8285-8296 ◽  
Author(s):  
N. Zhang ◽  
X. Zhou ◽  
S. Bertman ◽  
D. Tang ◽  
M. Alaghmand ◽  
...  
Keyword(s):  
Measurement Technique ◽  
Forest Canopy ◽  
Sonic Anemometer ◽  
Flux Measurement ◽  
Measurement Systems ◽  
Ambient Concentration ◽  
Solar Noon ◽  
Absorption Photometer ◽  
Upward Flux ◽  
Northern Michigan

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 Na2CO3-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 FHONO) 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 [NOx] and daytime HONO flux and between JNO2 × [NO2] and HONO flux, suggesting that NOx was not an important precursor responsible for HONO daytime production on the forest canopy surface in this low-NOx rural environment. Evidence supports the hypothesis that photolysis of HNO3 deposited on the forest canopy surface is a major daytime HONO source.

scholarly journals Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy

2012 ◽  
Vol 12 (3) ◽  
pp. 7273-7304 ◽  
Author(s):  
N. Zhang ◽  
X. Zhou ◽  
S. Bertman ◽  
D. Tang ◽  
M. Alaghmand ◽  
...  
Keyword(s):  
Measurement Technique ◽  
Forest Canopy ◽  
Sonic Anemometer ◽  
Flux Measurement ◽  
Rural Environment ◽  
Measurement Systems ◽  
Ambient Concentration ◽  
Solar Noon ◽  
Upward Flux ◽  
Northern Michigan

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 an optical fiber spectrometer with a 1-m long path flow cell. A Na2CO3-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 2-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 FHONO) 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 maximum mean of ~0.7 × 10−6 moles m−2 h−1 around solar noon, contributing a major fraction (~60%) to the HONO source strength required to sustain the observed ambient concentration of ~70 pptv. There was no significant correlation between NOx and daytime HONO flux, suggesting that NOx was not an important precursor responsible for HONO daytime production on the forest canopy surface in the low-NOx rural environment. Evidence suggests that photolysis of HNO3 deposited on the forest canopy surface is a major daytime HONO source.

Uncertainty in ammonia flux measurement systems

2004 ◽  
Author(s):  
Cale N Boriack ◽  
S.C. Capareda ◽  
R.E. Lacey ◽  
A Mutlu ◽  
S Mukhtar ◽  
...  
Keyword(s):  
Flux Measurement ◽  
Measurement Systems ◽  
Ammonia Flux

scholarly journals Hypertemporal Imaging Capability of UAS Improves Photogrammetric Tree Canopy Models

2020 ◽  
Vol 12 (8) ◽  
pp. 1238 ◽  
Author(s):  
Andrew Fletcher ◽  
Richard Mather
Keyword(s):  
Forest Canopy ◽  
Near Infrared ◽  
Spectral Band ◽  
Point Clouds ◽  
Tree Canopy ◽  
Solar Elevation ◽  
Spectral Bands ◽  
Eucalyptus Forest ◽  
Dense Point ◽  
Solar Noon

Small uncrewed aerial systems (UASs) generate imagery that can provide detailed information regarding condition and change if the products are reproducible through time. Densified point clouds form the basic information for digital surface models and orthorectified mosaics, so variable dense point reconstruction will introduce uncertainty. Eucalyptus trees typically have sparse and discontinuous canopies with pendulous leaves that present a difficult target for photogrammetry software. We examine how spectral band, season, solar azimuth, elevation, and some processing settings impact completeness and reproducibility of dense point clouds for shrub swamp and Eucalyptus forest canopy. At the study site near solar noon, selecting near infrared camera increased projected tree canopy fourfold, and dense point features more than 2 m above ground were increased sixfold compared to red spectral bands. Near infrared (NIR) imagery improved projected and total dense features two- and threefold, respectively, compared to default green band imagery. The lowest solar elevation captured (25°) consistently improved canopy feature reconstruction in all spectral bands. Although low solar elevations are typically avoided for radiometric reasons, we demonstrate that these conditions improve the detection and reconstruction of complex tree canopy features in natural Eucalyptus forests. Combining imagery sets captured at different solar elevations improved the reproducibility of dense point clouds between seasons. Total dense point cloud features reconstructed were increased by almost 10 million points (20%) when imagery used was NIR combining solar noon and low solar elevation imagery. It is possible to use agricultural multispectral camera rigs to reconstruct Eucalyptus tree canopy and shrub swamp by combining imagery and selecting appropriate spectral bands for processing.

Comparisons of surface flux measurement systems used in FIFE 1989

1992 ◽  
Vol 97 (D17) ◽  
pp. 18697 ◽  
Author(s):  
L. J. Fritschen ◽  
P. Qian ◽  
E. T. Kanemasu ◽  
D. Nie ◽  
E. A. Smith ◽  
...  
Keyword(s):  
Flux Measurement ◽  
Surface Flux ◽  
Measurement Systems

Advanced Industrial Measurement Systems for Productive Shipbuilding

1991 ◽  
Vol 7 (02) ◽  
pp. 106-117
Author(s):  
Albert W. Horsmon ◽  
Charles J Lupica
Keyword(s):  
Measurement Technique ◽  
Laser System ◽  
Measurement Techniques ◽  
Production Cycle ◽  
General Description ◽  
Modular Construction ◽  
Measurement Systems ◽  
Optical Laser ◽  
Industrial Measurement ◽  
Interim Products

Modern shipbuilders have embraced the concept of modular construction and are realizing the gains in productivity associated with this method. Further gains in productivity are achieved if these modules are built and erected "neat," that is, without the traditional excess material normally trimmed at erection. Construction of "neat" hull blocks requires rigid control of accuracy throughout the production cycle. Interim products, from fabricated parts to erected hull blocks, must be measured to acceptable tolerances to prevent excessive rework. This paper analyzes viable types of advanced measurement techniques supporting the process requirements of "neat" modular construction. Documentation of costs and difficulties associated with each measurement technique selected are also analyzed. The first part of the paper is a general description and analysis of the systems. The second part describes actual demonstrations of three measurement systems and analyzes them in the shipbuilding environment: digital theodolites, automated photogrammetry, and an optical laser system.

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