Identification of geostationary satellites using polarization data from unresolved images

In order to protect critical military and commercial space assets, the United States Space Surveillance Network must have the ability to positively identify and characterize all space objects. Unfortunately, positive identification and characterization of space objects is a manual and labor intensive process today since even large telescopes cannot provide resolved images of most space objects. Since resolved images of geosynchronous satellites are not technically feasible with current technology, another method of distinguishing space objects was explored that exploits the polarization signature from unresolved images. The objective of this study was to collect and analyze visible-spectrum polarization data from unresolved images of geosynchronous satellites taken over various solar phase angles. Different collection geometries were used to evaluate the polarization contribution of solar arrays, thermal control materials, antennas, and the satellite bus as the solar phase angle changed. Since materials on space objects age due to the space environment, it was postulated that their polarization signature may change enough to allow discrimination of identical satellites launched at different times. The instrumentation used in this experiment was a United States Air Force Academy (USAFA) Department of Physics system that consists of a 20-inch Ritchey-Chrétien telescope and a dual focal plane optical train fed with a polarizing beam splitter. A rigorous calibration of the system was performed that included corrections for pixel bias, dark current, and response. Additionally, the two channel polarimeter was calibrated by experimentally determining the Mueller matrix for the system and relating image intensity at the two cameras to Stokes parameters S0 and S1. After the system calibration, polarization data was collected during three nights on eight geosynchronous satellites built by various manufacturers and launched several years apart. Three pairs of the eight satellites were identical buses to determine if identical buses could be correctly differentiated. When Stokes parameters were plotted against time and solar phase angle, the data indicates that there were distinguishing features in S0 (total intensity) and S1 (linear polarization) that may lead to positive identification or classification of each satellite.

The presence of a woman : images of La Malinche in el Lienzo de Tlaxcala

La Malinche’s serene face and beautifully dressed figure dominates the first half of the lost sixteenth century manuscript El Lienzo de Tlaxcala, which exists today in the form of a copy made after the original. In this paper I propose an expanded study of these twenty-one representations of La Malinche as they offer insight into the Tlaxcalan’s reverence, respect, and spiritual belief in La Malinche. The Tlaxcalan leaders recognized her influence on both the Spanish and indigenous leaders during the conquest and cleverly designed a painted narrative to reinforce their connection with La Malinche to enhance their position with the Spanish. Through a multi layered study that consists of a detailed account of her biography in contrast to gender roles in Pre-Hispanic America, as well as formal and iconographic analysis of rarely examined images from the Lienzo de Tlaxcala that link La Malinche to the Virgin Mary, and a review of the ethnographic research on religious beliefs among contemporary Tlaxcalans, I will demonstrate that the mutable history of this woman made her the ideal supernatural protagonist for the people of Tlaxcala.