tailieunhanh - Soil and Environmental Analysis: Modern Instrumental Techniques - Chapter 11

Phạm vi của vấn đề môi trường phải đối mặt với chúng tôi và thực hiện những vấn đề rất phức tạp đã tạo ra một tình huống mà trong đó, các nhà khoa học từ một số môn ngày càng thấy mình hợp tác để điều tra một số vấn đề của đất-thực vật-không khí trao đổi. Chương này bàn về các phương pháp có thể được sử dụng ở quy mô của cảnh quan nông nghiệp. Các phương pháp thuộc lĩnh vực chung của micrometeorology rằng họ có thời gian và quy mô không gian mà là thứ. | 11 Measurement of Trace Gases II Micrometeorological Methods at the Plot-to-Landscape Scale John B. Moncrieff The University of Edinburgh Edinburgh Scotland I. INTRODUCTION The range of environmental concerns that face us and the realization that the issues are complex have produced a situation in which scientists from a number of disciplines increasingly find themselves collaborating to investigate some issue of soil-vegetation-atmosphere exchange. This chapter discusses the methods that can be used at the scale of the agricultural landscape. The methods belong to the general field of micrometeorology in that they have time and space scales that are on the order of tens of minutes and a few km2 respectively. The space scale is influenced both by the length scales of atmospheric turbulence which are a result of mechanical surface friction effects and by thermal effects which influence atmospheric stability. The reporting time scale for surface fluxes of about 30 min is related to the need to make observations over a suitably long period so that the majority of the spectra of flux-carrying eddies are sampled yet not so long that natural diurnal variabilities in scalar concentrations or forcing functions such as solar radiation are included. One important difference between micrometeorological methods and other techniques to measure surface fluxes is that they are nondestructive in that they only sample the air as it advects past the sensor they also are noncontact in that we merely sample passively as the air passes our instrumentation they cannot alter the microclimate as chamber methods MABCBL Copyright n 2004 by Marcel Dekker Inc. All Rights Reserved. for instance could do see Chap. 10 . Traditionally micrometeorologists have sought to establish their measuring systems on landscapes that are as flat as possible and with homogeneous surface cover as far as possible upwind. The earliest micrometeorological experiments were made over surfaces such as extensive wheat