Types Of Vertical Profiles Research Articles

Correlating the Horizontal and Vertical Distribution of LiDAR Point Clouds with Components of Biomass in a Picea crassifolia Forest

Light detection and ranging (LiDAR) has been widely used to estimate forest biomass. In this study, we aim to further explore this capability by correlating horizontal and vertical distribution of LiDAR data with components of biomass in a Picea crassifolia forest. Airborne small footprint full-waveform data were decomposed to acquire higher density point clouds. We calculated LiDAR metrics at the tree level and subplot level and correlated them to biomass components, including branch biomass (BB), leaf biomass (LB) and above-ground biomass (AGB), respectively. A new metric (Horizcv) describing the horizontal distribution of point clouds was proposed. This metric was found to be highly correlated with canopy biomass (BB and LB) at the tree level and subplot level. Correlation between AGB and Horizcv at the subplot level is much lower than that at tree level. AGB for subplot is highly correlated with the mean height metric (Hmean), canopy cover index (CCI) and the product of them. On the other hand, the relationship between the vertical distribution of LiDAR point and biomass was explored by developing two types of vertical profiles, including LiDAR distribution profiles and a biomass profile. Good relationships were found between these two types of vertical profiles and assessed by Pearson’s correlation coefficient (R) and the area of overlap index (AOI). These good correlations possess potential in predicting the vertical distribution of canopy biomass. Overall, it is concluded that not only the vertical, but also the horizontal distribution of LiDAR points should be taken into account in estimating components of biomass by LiDAR.

Atmospheric input and concentration of dissolved iron in the surface layer of the Gulf of California

A survey was conducted to determine the atmospheric input of particulate iron (Fep) and the factors and processes controlling the concentration and distribution of dissolved iron (Fed) in surface water (200 m) of the central Gulf of California. Atmospheric fluxes of Fep (7.0–90.4 µmol m–2 d–1) were of the same order of magnitude as those reported for the Red Sea (1.5–116 µmol m–2 d–1) and the northeastern Pacific Ocean (24 µmol m–2 d–1), but higher than the fluxes registered for the northwestern Mediterranean Sea (0.25–0.49 µmol m–2 d–1). According to the Fed concentration in surface water, three different zones were identified in the study area: a northern zone with Fed surface enrichment (5.57–7.21 nM) due to atmospheric input, a central zone with dilution of the Fed-enriched surface water by enhanced vertical mixing (0.07–0.59 nM), and a southern zone showing low Fed concentrations (less than 1 nM) due to biological uptake. Two types of vertical profiles were observed: (1) the typical nutrient-like distribution (with low concentrations at the surface and subsequent increase with depth) in the southern zone, and (2) mixed distribution (surface enrichment, decrease at subsurface level, and increase with depth) in the northern zone. The northern profile was 23.5 times more enriched than the adjacent Northeastern Pacific. Results indicate that Fed distribution in the surface layer of the central Gulf of California is controlled by complex interactions involving atmospheric input, biological uptake, and in situ removal-remineralization of particles, coupled with physical transport and vertical mixing.

Iridium in the Bering Sea and Arctic Ocean studied by neutron activation analysis

Neutron activation analysis combined with pretreatment based on anion-exchange was applied to the determination of Ir in the Bering Sea and Arctic Ocean seawaters. Separation and enrichment of Ir from seawater by a simple anion-exchange resin Bio-Rad AG1×8 was carried out prior to neutron activation. Ir concentrations in the vertically distributed Bering Sea and Arctic Ocean seawater samples were in range of 0.85–3.58 pg/l and 1.26–1.97 pg/l, respectively. The reagent blanks of the procedures were 0.42–0.60 pg Ir. It was found that Ir in the Bering Sea and in the Arctic Ocean displayed different types of vertical profiles.

Actinium-227 as a deep-sea tracer: sources, distribution and applications

Actinium is one of the rarest naturally occurring elements on earth. We measured its longest-lived isotope 227Ac (half-life 21.77 yr) for the first time in the water column of the Southeast Pacific, the Central Arctic, the Antarctic Circumpolar Current (ACC) and the Weddell Gyre (WG). Besides the profile in the Southeast Pacific, which confirms earlier findings about the role of diapycnal mixing for 227Ac distribution, we found three other different types of vertical profiles. These profiles point to a prominent role of advection for 227Ac distribution, especially in the Southern Ocean. Depending on the type of profile found, 227Ac is proposed as a tracer for different oceanographic questions. In the Southern Ocean, up to 4.93±0.32 dpm m −3 227Ac is found close to the sea floor, which is the highest concentration ever observed in the ocean. Close to the sea surface in the WG, 0.46±0.05 dpm m −3 227Ac ex ( 227Ac in excess of its progenitor 231Pa) is detected. We use 227Ac ex there to determine the upwelling velocity in the Eastern WG to be about 55 m yr −1. In the ACC, Upper and Lower Circumpolar Deep Water (UCDW and LCDW) are found to differ clearly in their 227Ac ex activity. High 227Ac ex activities are therefore a promising tracer for recent inputs of LCDW to the sea surface, which may help to understand the role of deep upwelling for iron inputs into Antarctic surface waters. The expected release of 227Ac is compared with 228Ra to make sure that the large near-surface excess in the water column of the Southern Ocean is not due to lateral inputs by isopycnal mixing. Data from the Central Arctic and from a transect across the ACC confirm that 228Ra and 227Ac ex differ strongly in their sources. The first measurements of 227Ac on suspended matter (less than 1.7% of total 227Ac close to the sea floor) indicate that the particle reactivity of 227Ac is negligible in the open ocean, in agreement with earlier findings [Y. Nozaki, Nature 310 (1984) 486–488]. Despite the extremely low concentrations of 227Ac, new measurement techniques [W.S. Moore, R. Arnold, J. Geophys. Res. 101 (1996) 1321–1329] point to a comfortable and comparably simple determination of 227Ac in the future. Finally, 227Ac ex may become a widely used deep-sea specific tracer.

Effects of stability on the profiles of vertical velocity and its variance in katabatic flow

The atmospheric katabatic flow in the foothills of the Front Range of the Rocky Mountains has been monitored by a network of towers and sodars for several years as part of the Atmospheric Studies in COmplex Terrain (ASCOT) program. We used three years of data from the network to explore the dependence on surface cooling and channeling by winds above the canyon of (1) profiles of the mean and variance of the vertical (perpendicular to the geopotential) component of motion and (2) the mean component of the wind perpendicular to the local terrain of Coal Creek Canyon. Previously we found that the magnitude of the near-surface temperature difference decreases with increasing surface cooling in light winds, apparently because of increasing turbulence caused when increasing drainage winds interact with surface topography. The variance of vertical velocity exhibits three types of vertical profiles, corresponding to different cooling rates and external wind speeds. The mean variance was found to depend strongly on a locally derived Richardson number.