Net Pan Research Articles

Is broad angular coverage necessary for echolocation-based discrimination involving aspect-dependent targets?

Building on the foundation of Dr. Whitlow Au’s pioneer and extensive work on the sonar of dolphins, recent research has illuminated the dynamic nature of echolocation involving free-swimming toothed whales. The sophisticated orchestration of movements and biosonar outputs by toothed whales is particularly relevant in the context of developing agile autonomous sonar-guided underwater vehicles. In this study, we test the hypothesis that broad angular coverage, which provide comprehensive echo information of aspect-dependent objects, is necessary for target discrimination via echolocation. We trained a harbor porpoise to actively approach and select a sphere against a spheroid in a two-alternative forced-choice target discrimination task in a net pan. Two spheroids of different aspect ratios representing two overall difficulty levels were used with each presented at diverse orientations when paired with the sphere. We show that the porpoise can discriminate these targets without acquiring aspect-dependent spheroid echo information over broad ranges of angles. Instead, focused, rapid sampling via buzzes appears to aid discrimination in more challenging scenarios. These results suggest that echolocation-based discrimination involving aspect-dependent objects is possible based on subsets of echo signatures without more extensive angular sampling that could build toward an understanding of the target identity. [Work supported by ONR.]

Estimating the fluctuation of Lake Hulun, China, during 1975–2015 from satellite altimetry data

Lake level, area, and volume changes can describe the fluctuation of water bodies. In this study, ICESat/Hydroweb and Landsat data recorded with irregularly time intervals from 1975 to 2015 were used to examine changes in lake level and area which were combined to indirectly estimate water volume variations of Lake Hulun. The time series of lake level, area, and volume variations of Lake Hulun exhibited a fluctuating trend from 1975 to 1984 and the mean value were about 542.57m, 2065.76km2, and -0.045km3, respectively and an increasing trends showed during 1984-2000. Lake Hulun revealed the fastest decrease in lake level (-0.42m/a), volume (-0.83km3/a) from 2000 to 2009, and the fastest shrinking in surface area (-33.88km2/a) during 2000-2012. There was a seasonal variation of water level and lake volume variations during 2009-2012 and the mean value were 539.98m and -5.72km3, respectively. From 2012 to 2015, a faster increasing trends were shown in water level, area, and volume variations with a rate of 0.73m/a (the amount of change was 2.92m), 81.95km3/a (the amount of change was 327.8km2), and 0.42km3/a (the amount of change was1.67km3), respectively. The lake level and area showed strong correlations for Lake Hulun (R 2=0.93). The water volume changes were in very good agreement for lake level changes (R 2>0.99) and surface area variations (R 2=0.92). Combining with lake level and area changes, the sum of lake volume variation of Lake Hulun was obtained and it showed a positive water budgets of 0.24km3 during past 40years. River and groundwater discharge, the pan evaporation, the net pan evaporation, and the water diversion project were reasons for the lake level, area, and volume variations in Lake Hulun. This study demonstrates that remote sensing data can be used as a source of information for monitoring comprehensively the fluctuation of large water bodies.

Impact of irrigation volume and water salinity on winter wheat productivity and soil salinity distribution

Sustainable development of agriculture in the North China Plain is severely restricted by a shortage of fresh water. Saline water used for irrigation can increase crop yields as well as the risk of soil salinization. Therefore, to identify safe and simple ways of using saline water in this region, field experiments were conducted from 2011 to 2013 to evaluate the effect of irrigation volume and water salinity on winter wheat productivity and soil salinity distribution. A total of twelve treatments including four levels of irrigation volume (0.8E, 1.0E, 1.2E and 1.4E) and three levels of water salinity (3.3, 5, and 6.8dSm−1) (S1, S2 and S3), were arranged in a randomized split-plot design with three replicates of each treatment. E is the total net pan evaporation that occurred after the irrigation. The results indicated that soil salinity increased at the harvest time of winter wheat under all of the treatments compared with initial conditions, particularly in the upper soil layers (0–40cm). However, these impacts were eliminated by rainfall in summer and autumn. The effect of irrigation water salinity on yield was significant in the 2011/2012 growing season and non-significant in the 2012/2013 growing season (p<0.05). Quadratic relationships were found between grain yield and irrigation volume for three water salinity levels in both growing seasons. The effects of irrigation volume on total water use (TWU), water productivity (WP) and irrigation water productivity (WPirrig) were significant. The interaction effects of irrigation volume and water salinity on grain yield, TWU, WP, WPirrig and soil salinity were statistically non-significant. The optimal irrigation volume per application was 0.98E, 0.98E and 0.92E for water salinities of S1, S2 and S3, respectively, by which more than 96% of the maximum yield and WP can be achieved.

A Nitrogen and Water Response Surface for Sprinkler‐Irrigated Broccoli1

AbstractFarmers typically apply large amounts of both N and water in commercial vegetable production. As costs of both inputs increase, and with mounting concern over nitrate leaching and non‐point source water pollution, the need for information on optimal management of both resources grows. We investigated the combined effects of five N application rates (0, 87, 190, 255, and 331 kg ha−1) and a continuous irrigation variable (1.14 to 32.9 cm of water, or 0.05 to 1.52 times net pan evaporation) applied by a line‐source sprinkler system on broccoli (Brassica oleraceaL., Botrytis group) growth rates and yield. Growth rates generally increased with both water and N treatments, although some interactions emerged. Harvested fresh weights continued to increase throughout the range of treatments, applied, with maximum yields in excess of 20 Mg ha−1. Yield (Mg ha−1) responded to N (kg ha−1) and water applied following seedling establishment (cm) according to the equation Y−1.03 + 0.0498 N− 8.73 × 10−5N2+ 1.23 × l0−3NW+ 0.272 W− 8.20 × 10−3W2, where Yis yield, Nis nitrogen, and Wis water applied after seedling establishment. Analysis of the resulting response surface indicated that under these conditions of frequent sprinkler irrigation (approximately twice weekly), relatively low N rates (140 kg ha−1) provided the lowest combined N and water cost for 10 Mg ha−1) yield. Further, yields increased with higher N and water rates, although quality must also be considered

The use of leaf development rate to determine time to irrigate pangola grass

The leaf development rate (LDR) of pangola grass (the number of new leaves produced on a shoot per unit of time) growing in swards on Cununurra Clay in the Ord Valley was found to decline linearly with cumulative net pan evaporation (+Ep) and ceased at a +Ep of 201 mm. The LDR of vegetative shoots, which have hairy nodes, was 3-5 times greater than that of reproductive shoots, which have glabrous nodes. Nitrogen increased the LDR of only the reproductive shoots. Vegetative shoots were preferred for measuring the response of pangola grass to moisture stress because of their insensitivity to nitrogen fertilizer level and faster LDR. Moisture availability (M) was calculated for each day as follows: M = 201 -+Ep for +Ep &lt; 201, or otherwise M = 0. In an irrigation trial covering two 3-month periods there was a linear relation between M and dry matter yield within each period, and at each of four N rates. It is suggested that LDR measurements could be used to determine irrigation frequency of pangola grass for any site where pan evaporation is also measured. On Cununurra Clay in the Ord Valley the most frequent irrigation schedule (every 2 weeks) gave the highest dry matter yields.