ALBERT

Description: Our previous study shows that the angle of linear polarization (AOLP) of solar radiation that is scattered from clouds at near-backscatter angles can be used to detect super-thin cirrus clouds over oceans. Such clouds are too thin to be sensed using any current passive satellite instruments that only measure light's total intensity, because of the uncertainty in surface reflection. In this report, we show that with a method similar to the super-thin cloud detection algorithm, dust aerosols may also be detected and differentiated from clouds. We also show that the degree of polarization of reflected light can be used for retrieving the optical depth of dust aerosols in the neighborhood of the backscatter angle, regardless of the reflecting surface conditions. This is a simple and robust algorithm, which could be used to survey dust aerosols over midlatitude and tropical oceans.

Description: This series of viewgraphs presents an introduction to the status of the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO),lessons learned during CALIPSO inclination maneuvers, the planning for CALIPSO's inclination maneuver to take place in 2009, examines a decision whether to precess or not, the plans to change CALIPSO's pitch, and the plans to change CALIPSO's pitch from the viewpoint of the payload.

Description: In this work, we demonstrate the feasibility and performance of photon sieve diffractive optical elements fabricated via a direct laser ablation process. Pulses of 50 ns width and wavelength 1064 nm from an ytterbium fiber laser were focused to a spot diameter of approximately 35 m. Using a galvanometric scan head writing at 100 mm/s, a 30.22 mm(exp 2) photon sieve operating at 633 nm wavelength with a focal length of 400 mm was fabricated. The optical performance of the sieve was characterized and is in strong agreement with numerical simulations, producing a focal spot size full-width at half-maximum (FWHM) of 45.12 0.74 m with a photon sieve minimum pinhole diameter of 62.2 m. The total time to write the photon sieve pattern was 28 seconds as compared to many hours using photolithography methods. We also present, for the first time to our knowledge in the literature, thorough characterization of the influence of angle of incidence, temperature, and illumination wavelength on photon sieve performance. Thus, this work demonstrates the potential for a high speed, low cost fabrication method of photon sieves that is highly customizable and capable of producing sieves with low or high numerical apertures.

Description: Over the past several decades, the need for high-resolution, high-efficiency, lightweight, high contrast focusing optics has continued to increase due to their applications in fields such as astronomy, spectroscopy, free-space optical communications, defense, and remote sensing. In recent years, photon sieve planar diffractive optics have been developed on flexible, lightweight polyimide substrates. However, transmission efficiencies have continuously been very low (~1-4%), thus impeding the widespread use of photon sieves in practical applications. Here, we present a flexible, lightweight, N = 4 level phase photon sieve with over 25% transmission efficiency; nearly triple that of any other photon sieve reported thus far. In this study, the photon sieve was fabricated via a novel pulsed laser ablation method using an ultraviolet source, and the total time to fabricate a ~3 sq cm sample was tens of seconds. Theoretical analysis of the photon sieve was carried out via the FDTD method, and was in very good agreement with experimental results. We also calculated via FDTD modeling the behavior of higher step (N = 8, 16, 32) photon sieves for further enhanced efficiencies, and show a fundamental limit on photon sieve efficiency of 70% in the limit of increasing step number. This multilevel photon sieve represents a new step in high-resolution diffractive optics, moving towards efficiencies suitable for widespread applications.

Description: vAs the potential impacts of global climate change become more clear [1], the need to determine the accuracy of climate prediction over decade-to-century time scales has become an urgent and critical challenge. The most critical tests of climate model predictions will occur using observations of decadal changes in climate forcing, response, and feedback variables. Many of these key climate variables are observed by remotely sensing the global distribution of reflected solar spectral and broadband radiance. These "reflected solar" variables include aerosols, clouds, radiative fluxes, snow, ice, vegetation, ocean color, and land cover. Achieving sufficient satellite instrument accuracy, stability, and overlap to rigorously observe decadal change signals has proven very difficult in most cases and has not yet been achieved in others [2]. One of the earliest efforts to make climate quality observations was for Earth Radiation Budget: Nimbus 6/7 in the late 1970s, ERBE in the 1980s/90s, and CERES in 2000s are examples of the most complete global records. The recent CERES data products have carried out the most extensive intercomparisons because if the need to merge data from up to 11 instruments (CERES, MODIS, geostationary imagers) on 7 spacecraft (Terra, Aqua, and 5 geostationary) for any given month. In order to achieve climate calibration for cloud feedbacks, the radiative effect of clear-sky, all-sky, and cloud radiative effect must all be made with very high stability and accuracy. For shortwave solar reflected flux, even the 1% CERES broadband absolute accuracy (1-sigma confidence bound) is not sufficient to allow gaps in the radiation record for decadal climate change. Typical absolute accuracy for the best narrowband sensors like SeaWiFS, MISR, and MODIS range from 2 to 4% (1-sigma). IPCC greenhouse gas radiative forcing is approx. 0.6 W/sq m per decade or 0.6% of the global mean shortwave reflected flux, so that a 50% cloud feedback would change the global reflected flux by approx. 0.3 W/sq m or 0.3% per decade in broadband SW calibration change. Recent results comparing CERES reflected flux changes with MODIS, MISR, and SeaWiFS narrowband changes concluded that only SeaWiFS and CERES were approaching sufficient stability in calibration for decadal climate change [3]. Results using deep convective clouds in the optically thick limit as a stability target may prove very effective for improving past data sets like ISCCP. Results for intercalibration of geostationary imagers to CERES using an entire month of regional nearly coincident data demonstrates new approaches to constraining the calibration of current geostationary imagers. The new Decadal Survey Mission CLARREO is examining future approaches to a "NIST-in-Orbit" approach of very high absolute accuracy reference radiometers that cover the full solar and infrared spectrum at high spectral resolution but at low spatial resolution. Sampling studies have shown that a precessing CLARREO mission could calibrate other geo and leo reflected solar radiation and thermal infrared sensors.