Abstract

There are three major sources of illumination on objects in the near Earth space environment: Sunshine, Moonshine, and Earthshine. For objects in this environment (satellites, orbital debris, etc.) known as Resident Space Objects (RSOs), the sun and the moon have consistently small illuminating solid angles and can be treated as point sources; this makes their incident illumination easily modeled. The Earth on the other hand has a large illuminating solid angle, is heterogeneous, and is in a constant state of change. The objective of this thesis was to characterize the impact and variability of observed RSO Earthshine on apparent magnitude signatures in the visible optical spectral region.

A key component of this research was creating Earth object models incorporating the reflectance properties of the Earth. Two Earth objects were created: a homogeneous diffuse Earth object and a time sensitive heterogeneous Earth object. The homogeneous diffuse Earth object has a reflectance equal to the average global albedo, a standard model used when modeling Earthshine. The time sensitive heterogeneous Earth object was created with two material maps representative of the dynamic reflectance of the surface of the earth, and a shell representative of the atmosphere. NASA’s Moderate-resolution Imaging Spectroradiometer (MODIS) Earth observing satellite product libraries, MCD43C1 global surface BRDF map and MOD06 global fractional cloud map, were utilized to create the material maps, and a hybridized version of the Empirical Line Method (ELM) was used to create the atmosphere. This dynamic Earth object was validated by comparing simulated color imagery of the Earth to that taken by: NASAs Earth Polychromatic Imaging Camera (EPIC) located on the Deep Space Climate Observatory (DSCOVR), and by MODIS located on the Terra satellite.

The time sensitive heterogeneous Earth object deviated from MODIS imagery by a spectral radiance root mean square error (RMSE) of ±14.86 [watts/m^2srμm] over a sample of ROIs. Further analysis using EPIC imagery found a total albedo difference of +0.03% and a cross correlation of 0.656. Also compared to EPIC imagery it was found our heterogeneous Earth model produced a reflected Earthshine radiance RMSE of ±28 [watts/m^2srμm] incident on diffuse spherical RSOs, specular spherical RSOs, and diffuse flat plate RSOs with an altitude of 1000km; this resulted in an apparent magnitude error of ±0.28. Furthermore, it was found our heterogeneous Earthmodel produced a reflected Earthshine radiance RMSE of ±68 [watts/m^2srμm] for specular flat plate RSOs with an altitude of 1000km; this resulted in an apparent magnitude error of ±0.68.

The Earth objects were used in a workflow with the Digital Imaging and Remote Sensing Image Generation (DIRSIG) tool to explore the impact of a range of characteristic RSO geometries, geographies, orientations, and materials on the signatures from an RSO due to Earthshine. An apparent magnitude was calculated and used to quantify RSO Earthshine signature variability; this is discussed in terms of the RMSE and maximum deviations of visible RSO Earthshine apparent magnitude signatures comparing the homogeneous Earth model to heterogeneous Earth model. The homogeneous diffuse Earth object was shown to approximate visible RSO Earthshine apparent magnitude signatures from spheres with a RMSE in reflected Earthshine apparent magnitude of ±0.4 and a maximum apparent magnitude difference of 1.09 when compared to the heterogeneous Earth model. Similarly for diffuse flat plates, the visible RSO Earthshine apparent magnitude signature RMSE was shown to be ±0.64, with a maximum apparent magnitude difference of 0.82. For specular flat plates, the visible RSO Earthshine apparent magnitude signature RMSE was shown to be ±0.97 with maximum apparent magnitude difference of 2.26.

This thesis explored only a portion of the parameter dependencies of Earth shine, but has enabled a preliminary understanding of visible RSO Earthshine signature variability and its geometric dependence. This research has demonstrated the impact of Earth heterogeneity on the observed apparent magnitude signatures of RSOs illuminated by Earthshine and the potential for error that comes with approximating the Earth as a diffuse homogeneous object.

Publication Date

6-1-2017

Document Type

Thesis

Student Type

Graduate

Degree Name

Imaging Science (MS)

Department, Program, or Center

Chester F. Carlson Center for Imaging Science (COS)

Advisor

Michael Gartley

Advisor/Committee Member

John Kerekes

Advisor/Committee Member

Rolando Raqueno

Campus

RIT – Main Campus

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