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Glacial acceleration is a main source of uncertainty in sea-level-change assessment. Measurement of ice-surface heights with a spatial and temporal resolution that not only allows elevation-change calculation, but also captures ice-surface morphology and its changes is required to aid in investigations of the geophysical processes associated with glacial acceleration. The Advanced Topographic Laser Altimeter System aboard NASA’s future ICESat-2 Mission (launch 2017) will implement multibeam micropulse photon-counting lidar altimetry aimed at measuring ice-surface heights at 0.7-m along-track spacing. The instrument is designed to resolve spatial and temporal variability of rapidly changing glaciers and ice sheets and the Arctic sea ice. The new technology requires the development of a new mathematical algorithm for the retrieval of height information. We introduce the density-dimension algorithm (DDA) that utilizes the radial basis function to calculate a weighted density as a form of data aggregation in the photon cloud and considers density an additional dimension as an aid in autoadaptive threshold determination. The autoadaptive capability of the algorithm is necessary to separate returns from noise and signal photons under changing environmental conditions. The algorithm is evaluated using data collected with an ICESat-2 simulator instrument, the Slope Imaging Multi-polarization Photon-counting Lidar, over the heavily crevassed Giesecke Braer in Northwestern Greenland in summer 2015. Results demonstrate that ICESat-2 may be expected to provide ice-surface height measurements over crevassed glaciers and other complex ice surfaces. The DDA is generally applicable for the analysis of airborne and spaceborne micropulse photon-counting| lidar data over complex and simple surfaces.

Methods to radiometrically calibrate a non-imaging airborne visible-to-shortwave infrared (VSWIR) spectrometer to measure the Greenland Ice Sheet surface are presented. Airborne VSWIR measurement performance is then benchmarked for bright Greenland ice and dark bare rock/soil targets using the MODerate resolution atmospheric TRANsmission (MODTRAN) radiative transfer code (version 6.0), and a coincident Landsat 8 Operational Land Imager (OLI) acquisition on 29 July 2015 during an in-flight radiometric calibration experiment. Airborne remote sensing flights were carried out in northwestern Greenland in preparation for the Ice, Cloud and land Elevation Satellite 2 (ICESat-2) laser altimeter mission. Nine science flights were conducted over the Greenland Ice Sheet, sea ice, and open ocean water. The campaign’s primary purpose was to correlate green laser pulse penetration into snow and ice with spectroscopic derived surface properties. An experimental airborne instrument configuration that included a nadir viewing (downward looking at the surface) non-imaging Analytical Spectral Devices Inc. (ASD) spectrometer that measured at-sensor upwelling VSWIR (0.35 to 2.5 µm) spectral radiance (Watts/m−2/sr−1/nm−1) in the two color Slope Imaging Multi-polarization Photon-Counting Lidar’s (SIMPL) ground Instantaneous Field-of-View, and a zenith viewing (upward looking at the sky) ASD spectrometer that measured at-sensor VSWIR spectral irradiance (Watts/m−2/nm−1) was flown. Rigorous radiometric calibration procedures for laboratory, in-flight, and field environments are described in detail to achieve a targeted at-sensor VSWIR measurement requirement of within 5 % to support calibration/validation (cal/val) efforts and geophysical science algorithm development. Our MODTRAN simulations for the 29 July flight line over dark and bright targets indicate that the nadir viewing airborne VSWIR spectrometer achieved an at-sensor spectral radiance measurement accuracy of between 0.6 and 4.7 % for VSWIR wavelengths (0.4 to 2.0 µm) with atmospheric transmittance greater than 80 %. At-sensor MODTRAN simulations for Landsat 8 OLI relative spectral response functions suggest that OLI is measuring 6 to 16% more at-sensor top-of-atmosphere (TOA) spectral radiance from the Greenland Ice Sheet surface than was observed from the nadir viewing airborne VSWIR spectrometer. While more investigation is required to convert airborne at-sensor VSWIR spectral radiance into atmospherically-corrected airborne surface reflectance, it is expected that airborne science flight data products will contribute to spectroscopic determination of Greenland Ice Sheet surface properties to improve understanding of their potential influence on ICESat-2 measurements.

In order to overcome spatial resolution limitations associated with physical sensor limitations when using smallsats and cubesats, we utilize an image processing technology referred to as Super-Resolution (SR). In general, software approaches are increasingly considered in connection with smaller satellites for which size, mass and power constraints limit the sensor capabilities. Being able to perform hardware vs. software trades might enable more capabilities for a lower cost. This paper describes recent experiments conducted to optimize the spatial enhancement of acquired observations using multiple sub-pixel shifted low resolution image.

For 46 years, the Landsat program has been providing continuous, consistent and high-quality data used routinely by decision makers both inside and outside the government, for a wide range of natural resource issues. In 2015, NASA Earth Science Technology Office (ESTO) has established the Sustainable Land Imaging Technology (SLI-T) Program to research, develop, and demonstrate new measurement technologies and reduced costs for future land imaging measurements. This paper provides information regard current SLI-T tasks to reach the program goals.

While there is growing interest in implementing future NASA Earth Science missions as Distributed Spacecraft Missions (DSMs), there are currently very few tools available to help in the design of DSMs. The objective of our project is to provide a framework that facilitates DSM Pre-Phase A investigations and optimizes DSM designs with respect to a-priori Science goals. Our Trade-space Analysis Tool for Constellations (TAT-C) enables the investigation of questions such as: “Which type of constellations should be chosen? How many spacecraft should be included in the constellation? Which design has the best cost/risk value?”. This paper provides a description of the TAT-C tool and its components.

The Landsat 9 mission, currently under development and proceeding towards a targeted launch in late 2020, will be very similar to the Landsat 8 mission, launched in 2013. Like Landsat 8, Landsat 9 is a joint effort between NASA and USGS with two sensors, the Operational Land Imager 2 (OLI-2), essentially a copy of the OLI on Landsat 8 and the Thermal Infrared Sensor 2 (TIRS-2), very similar to the TIRS on Landsat 8. The OLI-2, like OLI, provides 14-bit image data, though for Landsat 9, all 14 bits will be retained and transmitted to the ground. The focal plane modules to be used for OLI-2 were flight spares for OLI and are currently being retested by Ball Aerospace. Results indicate radiometric performance comparable to OLI. The TIRS was a class C instrument, with a 3-year design lifetime, and therefore had limited redundancy. TIRS-2 will be a class B instrument, with a 5-year design lifetime, like OLI (and OLI-2), necessitating design changes to increase redundancy. The stray light and Scene Select Mechanism (SSM) encoder problems observed on orbit with TIRS have also instigated a few design changes to TIRS-2. Stray light analysis and testing have indicated that additional baffles in the TIRS-2 optical system will suppress the out-of-field response. The SSM encoder problems have not been definitively traced to a route cause, though conductive anodic filament growth in the circuit boards is suspected. Improved designs for the encoder are being considered for TIRS-2. The spare Focal Plane Array (FPA) from TIRS is planned for use in TIRS-2; FPA spectral and radiometric performance testing is scheduled for September of this year at NASA's Goddard Space Flight Center.

The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) is a polarimetric, two-color, multi-beam push broom laser altimeter developed through the NASA Earth Science Technology Office Instrument Incubator Program. It has flown successfully on multiple airborne platforms beginning in 2008.1 It was developed to demonstrate new altimetry capabilities that combine height measurements and information about surface composition and properties. In this talk we will discuss the laser transmitter design and performance and present recent science data collected over the Greenland ice sheet and arctic sea ice in support of the second NASA Ice Cloud and land Elevation Satellite (ICESat-2) mission to be launched in 2017.2

The Operational Land Imager (OLI) routinely acquires calibration datasets involving various targets such as the solar diffusers collects, Pseudo Invariant Calibration Sites (PICS), and Lunar collects. This paper focus on stray light analysis of the lunar collects made through the lifetime of the mission. The analysis done on the lunar collects is used to estimate stability of stray light levels from which the stability or built up of contamination is demonstrated.

The Operational Land Imager (OLI) aboard the LDCM satellite was rigorously radiometrically characterized prior to launch to assure absolute calibration that is NIST traceable. On orbit additional dedicated calibration collects are being made to continue monitoring and characterizing the OLI radiometric performance. In this paper we report on the OLI on-orbit uniformity performance, which is a natural extension of the absolute radiometric accuracy. Such performance characteristic in remote sensing instruments is assuring that the radiometric accuracy in low contrast images is preserved while avoiding non-uniformity artifacts in the produced radiometric product. The LDCM project science team working with the instrument teams developed a performance metric to monitor the uniformity performance. We will describe the uniformity performance metric and discuss associated error sources in obtaining the radiometric calibration parameters that impact the uniformity correction. We will compare the uniformity performance between solar diffuser observation and earth data.

Hyperspectral, multiangle reflected radiances were obtained using the airborne advanced solid-state array spectroradiometer (ASAS)over Boreal Ecosystem-Atmosphere Study (BOREAS) sites in Canada during four field campaigns in 1994. Atmospherically corrected bidirectional reflectance factors and estimates of spectral hemispherical reflectance for three canopies in the BOREAS southern study area (old aspen, old black spruce, and old jack pine) are presented. The multiangle spectral reflectance factors derived from data acquired July 21, 1994 (for a limited solar zenith angle range of 34°–37°) for the forested sites showed distributions of high backscatter and consistently low forward scatter due to shadowing. Position and shape of the retrosolar maximums for the three sites varied. Spectral distinction among the sites was evident in the red, where reflectance factors for the jack pine exceeded those for spruce and aspen, and in the near infrared (NIR), where the aspen reflectance factors were twice those for the conifers. Data presented here suggest that spectral reflectances acquired at 26° backscatter in the principal plane would provide better discrimination among the major cover types than those obtained from a nadir view. Red reflectance was strongly dependent on view geometry for the spruce and jack pine sites due to the varying amounts of deep shadow and red-reflecting materials observed as a function of view azimuth and zenith. At the aspen site the red reflectance displayed much less variation with changing view zenith and azimuth. Accordingly, angular effects on the normalized difference vegetation index were large for the spruce and jack pine canopies but small for the aspen site. Estimated spectral hemispherical reflectances for photosynthetically active radiation (PAR) (0.4–0.7 μm), red (0.63–0.69 μm), and NIR (0.83–0.87 μm) calculated using various combinations of azimuthal data sets as input to the Walthall et al. [1985] model showed the following trends: maximum estimates were generated using data from the solar principal plane (spp) only; minimum values were derived from perpendicular plane data and amounted to 50–83% (relative) of the corresponding spp value; and inclusion of data from three view azimuths together (spp + perpendicular + oblique) produced intermediate values totaling 73–91% (relative) of the spp result. A preliminary review of ASAS-derived and independent ground-based measures of PAR hemispherical reflectance revealed a sizable range in this parameter.

The newly launched Operational Land Imager (OLI) aboard the LDCM satellite has stringent prescription on the levels of ghosting and diffuse stray-light in the reflective bands in order to preserve the mission radiometric requirements. The LDCM project science team and instrument teams wrote the requirements such that they were image based, inclusive of all effects that appear to be ghosts or stray-light, and consequently more directly testable. The OLI Instrument Developer, Ball Aerospace Technology Corporation (BATC), working closely with experts from aerospace, academia, and the NASA/USGS LDCM project were able to identify and mitigate the various contributors to ghosting and stray-light, resulting in outstanding imagery for the wide field-of-view push-broom imaging sensor. We will describe the ghosting and stray-light requirements and some of the contributing effects such as the leaky pixels that were seen on the EO-1/ALI. We will also highlight some of the technical challenges encountered and the solutions resulting in the substantial reduction of ghosting and stray-light which were verified by ground test. We will compare these ground measurements and analytic predictions with Lunar scan data to, potentially, resolve the question of whether the source of some of the performance outliers was the instrument or the test equipment.

The Landsat Data Continuity Mission (LDCM) is being developed by NASA and USGS and is currently planned for launch in January 2013 [1]. Once on-orbit and checked out, it will be operated by USGS and officially named Landsat-8. Two sensors will be on LDCM: the Operational Land Imager (OLI), which has been built and delivered by Ball Aerospace & Technology Corp (BATC) and the Thermal Infrared Sensor (TIRS)[2], which was built and delivered by Goddard Space Flight Center (GSFC). The OLI covers the Visible, Near-IR (NIR) and Short-Wave Infrared (SWIR) parts of the spectrum; TIRS covers the Thermal Infrared (TIR). This paper discusses only the OLI instrument and its pre-launch characterization; a companion paper covers TIRS.

The Landsat Data Continuity Mission (LDCM) will have two pushbroom Earth-imaging sensors: the Operational Land Imager (OLI) and the Thermal InfraRed Sensor (TIRS). The OLI has the reflective 30-meter and panchromatic 15-meter ETM+ bands plus additional 30-meter bands at 443 nm and 1375 nm. The TIRS has two 100-meter bands that spectrally split the ETM+ thermal band. OLI has completed performance testing and is scheduled for a late summer 2011 delivery to the spacecraft. OLI radiometric performance has shown that polarization sensitivity is 1-2%; Signal-to-Noise Ratios at signal levels about 5-10% of full scale are between 6-12 times better than ETM+, e.g., 250 versus 30; radiometric stability over 16 days is better than 0.5% (2-sigma); coherent noise is not visible; detector operability is 100% (no dead or inoperable detectors), absolute radiance calibration uncertainty is ~4%, reflectance calibration uncertainty is ~2.5% and detector-to-detector radiometric uniformity is generally better than 0.5%. TIRS completed initial performance testing in March 2011 and in August 2011 will be entering its primary thermal vacuum performance testing with the integrated instrument. At this point indications are that the TIRS instrument will have noise levels roughly ¼ of the ETM+ bands and detector-to-detector radiometric uniformity of better than 0.5%.

Laser altimeter measurements of forest stands with distinct structures and compositions have been acquired at 532 nm (green) and 1064 nm (near-infrared) wavelengths and parallel and perpendicular polarization states using the Slope Imaging Multi-polarization Photon Counting Lidar (SIMPL). The micropulse, single photon ranging measurement approach employed by SIMPL provides canopy structure measurements with high vertical and spatial resolution. Using a height distribution analysis method adapted from conventional, 1064 nm, full-waveform lidar remote sensing, the sensitivity of two parameters commonly used for above-ground biomass estimation are compared as a function of wavelength. The results for the height of median energy (HOME) and canopy cover are for the most part very similar, indicating biomass estimations using lidars operating at green and near-infrared wavelengths will yield comparable estimates. The expected detection of increasing depolarization with depth into the canopies due to volume multiple-scattering was not observed, possibly due to the small laser footprint and the small detector field of view used in the SIMPL instrument. The results of this work provide pathfinder information for NASA's ICESat-2 mission that will employ a 532 nm, micropulse, photon counting laser altimeter.

A new remote sensing instrument, the Airborne Laser Polarization Sensor (ALPS), is making the first multispectral radiometric and polarization measurements of the Earth's surface using a polarized laser light source. Results from data flights taken over boreal forests in Maine at 1060 and 532 nm, using a Nd:YAG laser source, showing depolarization signatures for three broadleaf and five coniferous tree species, are discussed. Measurements made over nonforest ground cover had a large dynamic range in depolarization values at both wavelengths. The ALPS system use twelve photomultiplier tube detectors configurable to measure desired parameters such as the total backscatter and the polarization state, including the azimuthal angle and ellipticity, at different ultraviolet to near-infrared wavelengths simultaneously. Measurements of the azimuth and ellipticity of the backscatter polarization were variable and no specific conclusions have yet been drawn. >

The Slope Imaging Multi-polarization Photon-counting Lidar is an airborne instrument developed to demonstrate laser altimetry measurement methods that will enable more efficient observations of topography and surface properties from space. The instrument was developed through the NASA Earth Science Technology Office Instrument Incubator Program with a focus on cryosphere remote sensing. The SIMPL transmitter is an 11 KHz, 1064 nm, plane-polarized micropulse laser transmitter that is frequency doubled to 532 nm and split into four push-broom beams. The receiver employs single-photon, polarimetric ranging at 532 and 1064 nm using Single Photon Counting Modules in order to achieve simultaneous sampling of surface elevation, slope, roughness and depolarizing scattering properties, the latter used to differentiate surface types. Data acquired over ice-covered Lake Erie in February, 2009 are documenting SIMPL's measurement performance and capabilities, demonstrating differentiation of open water and several ice cover types. ICESat-2 will employ several of the technologies advanced by SIMPL, including micropulse, single photon ranging in a multi-beam, push-broom configuration operating at 532 nm.

The Operational Land Imager (OLI) on the Landsat Data Continuity Mission (LDCM) has a comprehensive radiometric characterization and calibration program beginning with the instrument design, and extending through integration and test, on-orbit operations and science data processing. Key instrument design features for radiometric calibration include dual solar diffusers and multi-lamped on-board calibrators. The radiometric calibration transfer procedure from NIST standards has multiple checks on the radiometric scale throughout the process and uses a heliostat as part of the transfer to orbit of the radiometric calibration. On-orbit lunar imaging will be used to track the instruments stability and side slither maneuvers will be used in addition to the solar diffuser to flat field across the thousands of detectors per band. A Calibration Validation Team is continuously involved in the process from design to operations. This team uses an Image Assessment System (IAS), part of the ground system to characterize and calibrate the on-orbit data.

More precise lunar and Martian ranging will enable unprecedented tests of Einstein's theory of general relativity as well as lunar and planetary science. NASA is currently planning several missions to return to the Moon, and it is natural to consider if precision laser ranging instruments should be included. New advanced retroreflector arrays at carefully chosen landing sites would have an immediate positive impact on lunar and gravitational studies. Laser transponders are currently being developed that may offer an advantage over passive ranging, and could be adapted for use on Mars and other distant objects. Precision ranging capability can also be combined with optical communications for an extremely versatile instrument. In this paper we discuss the science that can be gained by improved lunar and Martian ranging along with several technologies that can be used for this purpose.

NASA Goddard Space Flight Center is developing a direct-detection free-space laser communications transceiver test bed. The laser transmitter is a master-oscillator power amplifier (MOPA) configuration using a 1060 nm wavelength laser-diode with a two-stage multi-watt Ytterbium fiber amplifier. Dual Mach-Zehnder electro-optic modulators provide an extinction ratio greater than 40 dB. The MOPA design delivered 10-W average power with low-duty-cycle PPM waveforms and achieved 1.7 kW peak power. We use pulse-position modulation format with a pseudo-noise code header to assist clock recovery and frame boundary identification. We are examining the use of low-density-parity-check (LDPC) codes for forward error correction. Our receiver uses an InGaAsP 1 mm diameter photocathode hybrid photomultiplier tube (HPMT) cooled with a thermo-electric cooler. The HPMT has 25% single-photon detection efficiency at 1064 nm wavelength with a dark count rate of 60,000/s at -22 degrees Celsius and a single-photon impulse response of 0.9 ns. We report on progress toward demonstrating a combined laser communications and ranging field experiment.

We report on progress in developing a new swath mapping laser altimeter measurement approach using multiple laser measurement beams, modulated fiber lasers, photon counting detectors, and event timers for future space missions.

More precise lunar and Martian ranging will enable unprecedented tests of Einstein's theory of General Relativity and well as lunar and planetary science. NASA is currently planning several missions to return to the Moon, and it is natural to consider if precision laser ranging instruments should be included. New advanced retroreflector arrays at carefully chosen landing sites would have an immediate positive impact on lunar and gravitational studies. Laser transponders are currently being developed that may offer an advantage over passive ranging, and could be adapted for use on Mars and other distant objects. Precision ranging capability can also be combined with optical communications for an extremely versatile instrument. In this paper we discuss the science that can be gained by improved lunar and Martian ranging along with several technologies that can be used for this purpose., Comment: 14 pages, 3 figures, To appear in the International Journal of Modern Physics D

The Advanced Solid-State Array Spectroradiometer (ASAS) is an airborne, off-nadir tilting, imaging spectroradiometer that acquires digital image data for 29 spectral bands in the visible and near-infrared. The sensor is used principally for studies of the bidirectional distribution of solar radiation scattered by terrestial surfaces. ASAS has acquired data for a number of terrestial ecosystem field experiments and investigators have received over 170 radiometrically corrected, multiangle, digital image data sets. A database of ASAS digital imagery has been established in the Pilot Land Data System (PLDS) at the NASA/Goddard Space Flight Center to provide access to these data by the scientific community. ASAS, its processed data, and the PLDS are described, together with recent improvements to the sensor system.

The design of a multispectral polarized laser system for characterizing the depolarization properties of the earth's surface is described. Using a laser as the light source, this airborne system measures the Stokes parameters of the surface to simultaneously arrive at the polarization degree, azimuthal angle, and ellipticity for each wavelength. The technology will be studied for the feasibility of expansion of the sensor to do surface polarization imaging. The data will be used in support of solar polarization studies and to develop laser radiometry as a tool in environmental remote sensing.