Application of the empirical line method (ELM) to calibrate the airborne Daedalus-CZCS scanner

Abstract

The present investigation aims at providing a reliable evaluation of the geometric and radiometric accuracy of the airborne Daedalus-Coastal Zone Color Scanner (CZCS), through cal/val techniques. To this aim, on November 2014, we accomplished a remote sensing campaign over the Peligna Valley (Italy). Together with the personnel of the III Nucleo Aereo of the Italian Coast Guard, based at the Pescara Airport, we deployed the Daedalus AA1268EM1 CZCS scanner on board the fixed-wing aircraft type ATR42MP and a ASD FieldSpec spectroradiometer for a simultaneous field survey. We used vicarious calibration and secondary non-parametric geometric correction to achieve absolute atmospheric correction and geometric calibration, respectively. Although the validation and calibration targets used in this study were similar in nature, correlation coefficients of the prediction equations between at-sensor radiance and ground reflectance were > 0.90 for each of the 10 CZCS wavebands and the independent error assessment demonstrate that the empirical line method can be applied to correct CZCS imagery with satisfactory results. ARTICLE HISTORY

The Effect of Building Facades on Outdoor Microclimate—Reflectance Recovery from Terrestrial Multispectral Images Using a Robust Empirical Line Method

“…Multiple images were taken normal to the Dulux and Spectralon targets at distances of 3.2 m and 1 m respectively. The target sizes satisfied the recommendations in the literature to be a minimum 3 to 10 times the sensor IFOV [87][88][89][90][91][92][93][94][95][96][97][98]132] to ensure that as many pixels as possible associated with each calibration target were selected [88] and to avoid atmospheric effects [87]. Each Dulux panel and the Spectralon target measured 293 (h) × 210 mm (w) and 127 × 127 mm respectively (with a single multi-step column measuring 30 mm (w) × 120 mm (h)).…”

“…However, higher reflectance samples (V3 (nominal reflectance 70%); V4 (75%) and V5 (60%) in Table 15) underestimate measured values. Underestimation of high-albedo surfaces by the EL method has been reported previously [94]. Sample V13, red Granite stone (nom.…”

“…Empirical (or "vicarious") radiometric calibration using in-situ reference targets of known spectral reflectance correlated to at-sensor radiance for each sensor waveband robustly accounts for atmospheric and illumination effects and produces acceptable radiance-to-reflectance conversion results [48,88]. Despite its widespread use the method is error prone if implemented without logistical and methodological considerations [88,94]. For many inexpensive, commercially available MS cameras the relationship between at-sensor spectral radiance and image DNs is not readily available [95,96], is onerous to obtain [48,97] and may be non-linear [98] and the unique camera response function-the gain and offset coefficients used to convert the radiance-as-electrical signal to output digital numbers [92]-requires determination before DNs can be converted to reflectance units [99,100].…”

“…For many inexpensive, commercially available MS cameras the relationship between at-sensor spectral radiance and image DNs is not readily available [95,96], is onerous to obtain [48,97] and may be non-linear [98] and the unique camera response function-the gain and offset coefficients used to convert the radiance-as-electrical signal to output digital numbers [92]-requires determination before DNs can be converted to reflectance units [99,100]. In this case, the reflectance-based calibration method can be used to predict at-sensor radiance (expressed as image DNs) by measuring the reflectance of a calibration target [94,100].…”

“…While studies using EL methods for reflectance recovery are increasingly common to derive vegetation characteristics in open fields ( [86] and references therein) the use of the EL method for reflectance recovery from urban surfaces is less common due to logistical and methodological challenges posed by urban areas [5] but interest in applications to man-made and urban surfaces is growing [94,103,104].…”