Title: TransCal – An Innovative, Highly Accurate, Transmissive Radiometric Calibration Approach
Presenting Author: Nathan Leisso
Organization: BAE Systems, Inc.
Co-Author(s): Tom Kampe

Abstract:
TransCal is an innovative calibration method which utilizes an optical element which can reversibly switch between a diffuse state and a transparent state as the first element of the optical system. The goal of the TransCal program is to enable the continuation of the precise solar diffuser radiometric calibration used extensively in the Landsat program to future imaging sensors, while reducing the size and complexity of the calibration subsystem. The TransCal Polymer Dispersed Liquid Crystal (PDLC) optical elements are composed of PDLC microdroplets encased in polymer matrix. The orientation of the LC molecules defines the optical, electrical, magnetic, and mechanical properties. The individual LC molecules are locally ordered within an LC microdroplet but the microdroplets are randomly aligned relative to each other. This creates a high-degree of optical scattering in the nominal diffuse state. The PDLC material in the TransCal device is flanked by optical-grade Fused Silica windows coated with a conductive layer of Indium Tin Oxide (ITO). This enables the application of a local electric field to preferentially orientate the individual LC molecules across all microdroplets and results in a transparent TransCal optical element. The initial development of the prototype TransCal optical elements consisted of an iterative build process with different materials to optimize the PDLC performance for the TransCal program goals. Optical performance testing has been conducted including spectral transmittance, Bidirectional Transmittance Distribution Function (BTDF), and transmitted wavefront. In addition, radiation testing, and temporal stability have been assessed. Finally, the TransCal concept was operationally tested with a sensor to demonstrate performance.