Transmissometers measure the transmission of light of a given wavelength over a known distance in seawater. Different types of particles and dissolved organic matter in the water absorb and reflect light of different wavelengths. We choose wavelengths for our instruments based on which particles we are studying. The wavelength we use the most is about 660 nanometers (red). Surprisingly and fortunately, the amount of dissolved salt in the water does not affect the transmission of light through it. Transmission through particle-free fresh water and salt water is the same. Changes in the transmission of light through water are primarily related to changes in the abundance and type of particles present. Most variations in transmission come from particles less than 20 microns in diameter. Large particles and aggregates larger than 500 microns in diameter are not abundant in the ocean. Only a few exist in 1000 milliliters of water, so they rarely appear in the small sensing volume of the transmissometer (45 milliliters). When they do, they appear as singular large values which we remove from our data. | Transmissometer [18K] |
The amount of attenuation of light (c) equals the sum of light scattering (b) and absorption (a).
It's as simple as a+b=c.
Measuring these values is not so simple.
Most attenuation results from light scattering. Phytoplankton, however, contain little packets of chlorophyll in their cells that act as sponges for light, allowing them to absorb energy and use it in photosynthesis. Thus, living phytoplankton absorb more light than other particles.
With an instrument that can measure light absorption and attenuation (the a-c meter), we can start to distinguish living phytoplankton from dead plankton and other particles without taking water samples.
Optical backscatter meter (OBS or Light scattering sensor (LSS) Light scattering is difficult to measure completely because light scatters in all directions and the angle of scattering depends on the particles' sizes. Furthermore, as soon as light bounces off of one particle it can bounce off of another. We cannot distinguish whether we are measuring primary, secondary, tertiary, or greater scattering. Nevertheless, small scattering meters have been made that are useful-especially in turbid water-as they provide a crude measure of the particle abundance in the water. Scattering meters project a beam of light into the water while a detector next to the light source measures the amount of light scattered back into it. The optical backscatter meter (OBS) built by Downing Associates and the light scattering sensor (LSS) built by SeaTech use an infrared light source and a detector for this purpose. To determine the amount of particulate matter in the water, these instruments (like transmissometers) have to be calibrated by filtering particles from a known volume of water and weighing them very precisely. | Optical backscatter meter (OBS) or Light scattering sensor (LSS) [11K] |
Thu Aug 16, 2018 7:34 pm by nguyendunghh2
» Dữ liệu về nhiệt độ và lượng mưa cho tất cả các tình Việt Nam theo từng năm
Mon Dec 29, 2014 8:28 pm by tieuminh2510
» Giới thiệu sơ lược về NoSQL
Fri Dec 26, 2014 10:23 pm by tieuminh2510
» Bio7 IDE dành cho các nhà sinh thái học
Wed Aug 27, 2014 1:00 pm by tieuminh2510
» Ứng dụng dành để mở file netCDF
Tue Jul 29, 2014 11:21 am by tieuminh2510
» Đánh giá ngập lụt nước mặt tại Anh quốc
Fri Jun 27, 2014 11:52 pm by tieuminh2510
» Tài nguyên về các mô hình tính toán rối từ NASA (Turbulence Modeling Resource)
Thu Jun 05, 2014 7:17 pm by tieuminh2510
» Tích hợp công cụ tìm kiếm với hơn 2 triệu đầu sách điện tử
Sun Jun 01, 2014 8:05 pm by tieuminh2510
» MATLAB Books Collection (Bô sưu tập sách hơn 900MB cho MATLAB)
Sun Jun 01, 2014 3:58 pm by tieuminh2510
» Số liệu các trạm do đạc toàn cầu và từ mô hình WAVEWATCH III
Mon May 19, 2014 11:12 pm by tieuminh2510
» DHI MIKE 2012 (URBAN + GIS + ZERO)
Sat May 17, 2014 8:24 pm by tieuminh2510
» File Viewer 1.02 (No InstallQ)
Wed May 14, 2014 6:12 pm by tieuminh2510
» Coastal Engineering Manual 2003
Wed May 14, 2014 11:27 am by tieuminh2510
» Cổng thông tin dữ liệu Hải Dương học (Viện Hải dương học Nha Trang)
Sun May 11, 2014 5:30 pm by tieuminh2510
» A Generic Algorithm for Waste collection Vehicle routing problem with Time windows and Conflicts
Tue May 06, 2014 1:29 pm by tieuminh2510
» Mực Nước Đại Dương
Tue Feb 25, 2014 12:18 am by letrongloi
» Các thí nghiệm trong cơ chất lỏng của MIT
Tue Nov 12, 2013 10:07 pm by tieuminh2510
» Tài liệu dòng chảy
Fri Nov 08, 2013 11:16 pm by be_un2002
» Dự báo nước dâng do bão sử dụng Delft3D
Wed Oct 02, 2013 10:13 pm by tieuminh2510
» Một ví dụ đơn giản về ứng dụng của ANN
Fri Aug 02, 2013 11:17 pm by tieuminh2510
» Đưa DEFLT3D vào ArcGIS
Fri Aug 02, 2013 11:15 pm by tieuminh2510
» Hướng dẫn sử dụng phần mềm iThink 9.0.2 (Stella)
Tue Jul 23, 2013 2:56 pm by HieuTran2503
» Phần mềm Stella
Tue Jul 23, 2013 2:55 pm by HieuTran2503
» Du học Đức
Sat Jul 20, 2013 3:37 am by profet
» Ứng dụng Litpack
Tue Jul 16, 2013 2:40 pm by namthinh2007
» Xin hỏi tên về 1 loài ốc lạ
Tue Jul 16, 2013 2:14 pm by namthinh2007
» Xin tài liệu về nước dâng do bão
Tue Jul 16, 2013 2:02 pm by namthinh2007
» Lý thuyết triều điều hòa
Sun Jul 07, 2013 6:01 pm by tieuminh2510
» The Earth's Atmosphere
Sat Jun 01, 2013 10:05 pm by giohungyen
» Hướng dẫn cách đưa ảnh từ GoogleEarth vào ArcGIS
Sun May 19, 2013 5:47 pm by Chutli