# Landsat Surface Product Validation Instrumentation:
## 1 Big MAC Overview
### Purpose
#### 1.1.2 Measurement Technologies
Finally, a DJI Mavic, with a high spatial resolution RGB camera was flown in order to produce an overall basemap of the entire site. imagery was performed using the SDSU-measured reflectance of the Labsphere Pernaflect panels to perform an empirical line-based calibration [22]. Pertinent to the thermal portion of this campaign, the MX-2 carries a cooled FLIR A6751 sc SLS thermal imaging sensor. The FLIR is a broadband radiometric temperature imaging sensor with a spectral range of 7.5-10 microns and was flown over the entire BigMAC site [20]. In addition to the UAS sensors, RIT also fielded several ground-based instruments for measuring surface temperature. Chief among these was a FTIR spectroradiometer, called the \(\mu\)FTIR (developed by Designs & Prototypes). The \(\mu\)FTIR is designed to collect spectral measurements from 2 to 16 \(\upmu\)m at a resolution of 6 cm\({}^{-1}\), and it has a measured noise equivalent delta temperature (\(N\)_E_T_) of less than 0.3 \({}^{\circ}\)C. The Hobo MX2204 TidbiT water temperature logger was used in the thermal pool targets [23]. These small units have an advertised accuracy of \(\pm\)0.2 \({}^{\circ}\)C over the operational range of 0-70 \({}^{\circ}\)C.  
The SPARC method employs convex mirrors to relay the image of the full solar disk to a sensor under test. Originally SPARC was developed as geometric and spatial reference points for deriving the point spread functions and modulation transfer functions of the sensor under test. However, SPARC also produces targets suitable for deriving the absolute calibration coefficients of remote sensing Earth systems in the solar reflective spectrum [24; 25]. By varying the number of mirrors in a target, as well as the reflectance and RoC, targets can be produced for a wide variety of at-aperture radiance levels suitable for airborne- or satellite-based sensors of different resolutions from centimeters (e.g., UAS) to larger footprints in the hundreds of meters or above. It should be noted that because the SPARC mirrors are designed to deliver reflected light from the full solar disc to the sensor aperture, the diameter of the SPARC mirror has no impact on the at-sensor radiance level produced by the target. The diameter only impacts the targets projected angular FOR at which the full disk of the sun is visible by the overflying sensor. Based on the sky conditions, the SPARC algorithm can also correct for any significant hemispherical sky radiance reflected by the convex mirror based on radiative transfer modeling or the ground measurements of the diffuse-to-global ratio (G) at the time the target is imaged and the known FOR [24]. As part of the BigMAC experiment, a number of mirror targets were deployed for the calibration and characterization of UAS and other satellite assets alongside the traditional diffuse reflectance techniques [26]. With the precise knowledge of mirror properties, atmospheric modeling, and appropriate measurements, it is possible to derive the absolute radiance associated with a SPARC target and a given sensor. The mirrors then serve as a SI-traceable point source [27]. A key factor of the SPARC design is that the full solar disk virtual image from each mirror is smaller than the mirror diameter and much smaller than the sensor IFOV, thus producing nearly ideal point sources but free of significant diffraction effects that would plague other methods utilizing pinhole point sources for solar calibration. Similarly, and of great utility for correcting imagery to bottom-of-atmosphere surface reflectance [26; 28], it is possible to derive a LER for a SPARC target. The LER represents the bidirectional reflectance factor corresponding to the ratio of the radiance reflected by the SPARC target in the particular direction of the imaging sensor to the radiance that would be reflected into the same direction by an ideal Lambertian target, with identical illumination having the area equivalent to a single-pixel. The ratios are defined so that an ideal Lambertian reflector has a total reflectance factor of 100%.