Measurement of Direct radiance, Global Horizontal Irradiance and Diffuse Horizontal Irradiance Using an In-line Diffuser
Direct and diffuse solar irradiance are important components in a wide variety of remote sensing applications including environmental and climate research. These measurements allow scientists to fully characterize light and energy affecting the environment. These are critical metrics when researching climate change subjects like glacial retreat and alternative energy sources like solar panels. It can also be used by environmental scientists studying biomes and measuring the amount of light reaching through a canopy. There is no shortage of applications for this data in environmental science, climate research, agriculture, and other industries. Spectral Evolution provides the tools to collect this data and supports the pursuit of better understanding of our rapidly changing environment.
Direct solar irradiance is the portion of solar radiation that travels straight from the sun to the Earth’s surface without being scattered or absorbed by the atmosphere. In contrast, diffuse solar irradiance is sunlight that has been scattered by atmospheric components such as air molecules, water vapor, dust, or clouds, and does not come directly from the solar disc. Global horizontal irradiance (GHI) is the total solar energy received on a horizontal surface and is the sum of both direct and diffuse irradiance. Downwelling total solar irradiance represents the total incoming solar radiation reaching the Earth’s surface, which plays a crucial role in influencing the planet’s weather, climate systems, and environment. Measuring both direct and diffuse solar irradiance provides valuable insights into how energy is transformed within the Earth-atmosphere system, supports the analysis and distribution of atmospheric properties, and helps validate satellite-based radiation measurements.
These measurements are made easy using a spectroradiometer like the NaturaSpec™ and a selection of accessories like a Gershun tube and an in-line cosine diffuser. An in-line diffuser allows measurement of 180° FOV. This makes it possible to measure total horizontal irradiance and diffuse solar irradiance when shaded. Direct solar irradiance can be measured using a Gershun tube giving a 1° FOV.
GHI=DHI+DNI*cos(z)
Global Horizontal irradiance (GHI), Diffuse Horizontal radiation (DHI), Direct Normal irradiance (DNI), z = solar zenith angle. https://cbe-berkeley.gitbook.io/clima/documentation/tabs-explained/sun-and-cloud/global-and-diffuse-horizontal-solar-radiation/global-diffuse-and-normal-solar-radiation-explained
Spectral Evolution field spectrometers, including the RS-3500, NaturaSpec, NaturaSpec™ Plus, and NaturaSpec™ Ultra, are well-suited for measuring both direct and diffuse solar irradiance. These ground-based instruments offer key advantages such as high spectral resolution, portability, and the ability to adjust the optical accessories between measurements and enabling fast, accurate, and convenient data collection in the field. In this study, field measurements were conducted using a NaturaSpec equipped with an in-line diffuser to capture diffuse solar irradiance and global horizontal irradiance as well as the Gershun tube to measure direct solar irradiance. The measurements were collected efficiently using a leveled tripod mount, pistol grip, Gershun tube, and in-line diffuser, allowing for stable and precise alignment. Data collection took only a few minutes, and the Darwin software quickly and easily processed the irradiance values, highlighting the instrument’s effectiveness and ease of use for field applications.
Global horizontal Irradiance collected with an in-line diffuser indicated with red, direct radiance spectra collected with the Gershun tube attachment indicated in green.
DARWin™ SP Data Acquisition software, which comes with every Spectral Evolution instrument provides a tool accessed by a pull-down menu for integrated energy measurement. The pull-down utility allows users to calculate integrated energy levels as a function of wavelength interval (user adjustable).
Global Horizontal Irradiance, Diffuse Horizontal Irradiance Integrated energy values.
