Passive shortwave remote sensing from the Ground

Deducing and attempting to quantify properties of aerosols and trace atmospheric gases from ground-based sensors on the Earth’s surface has a long and interesting history that provided the foundation for the general field now known as “Remote Sensing”. The method utilizes measurements of the attenuation of light passing through the atmosphere, often taken at multiple wavelengths and sometimes broken down into spectral high resolution. Today, the method based on measuring attenuation of the direct beam is supplemented with measures of the intensity (radiance) or polarization of scattered light from the sun taken at different angles. Using the direct beam measurements to infer aerosol optical thickness is described in Chapter 4. The inversion methods applied to both direct beam and to angular measurements of the diffuse light are described in Chapter 5. In this chapter, we provide a history of ground-based aerosol remote sensing networks, leaving the formalism of the retrievals and inversions to the previous chapters. Not described in detail in this book are methods to retrieve trace gas measurements using absorption features measured by groundbased sensors, even though the history of trace gas measurements and aerosol measurements go hand-in-hand. Remote sensing by ground-based sensors can provide information about the spectral aerosol optical thickness, particle size distribution, aerosol absorption and degree of nonsphericity of the particles. The techniques often impose great demands on precision and accuracy. The history of ground-based remote sensing networks is plagued with good intentions that were stymied by the lack of consistent and reliable calibration that could assure the necessary precision and accuracy.