Veljko M. Jovanovic

First results from a dual photoelastic-modulator-based polarimetric camera

We report on the construction and calibration of a dual photoelastic-modulator (PEM)-based polarimetric camera operating at 660?nm. This camera is our first prototype for a multispectral system being developed for airborne and spaceborne remote sensing of atmospheric aerosols. The camera includes a dual-PEM assembly integrated into a three-element, low-polarization reflective telescope and provides both intensity and polarization imaging. A miniaturized focal-plane assembly consisting of spectral filters and patterned wire-grid polarizers provides wavelength and polarimetric selection. A custom push-broom detector array with specialized signal acquisition, readout, and processing electronics captures the radiometric and polarimetric information. Focal-plane polarizers at orientations of 0 degrees and -45 degrees yield the normalized Stokes parameters q=Q/I and u=U/I respectively, which are then coregistered to obtain degree of linear polarization (DOLP) and angle of linear polarization. Laboratory test data, calibration results, and outdoor imagery acquired with the camera are presented. The results show that, over a wide range of DOLP, our challenging objective of uncertainty within +/-0.005 has been achieved.

MISR in-flight camera geometric model calibration and georectification performance

In order to facilitate a unique georectification approach implemented for Multi-angle Imaging SpectroRadiometer (MISR) data, specific calibration datasets need to be derived during flight. In the case of the spaceborne MISR instrument, with its unique configuration of nine fixed pushbroom cameras, continuous and autonomous coregistration and geolocation of image data are required prior to the application of scientific retrieval algorithms. In-flight-generated calibration datasets are required to (a) assure accuracy, (b) reduce processing load, and (c) support autonomous aspects of the processing algorithm. This paper describes the in-flight geometric calibration approach with the focus on the first year of activities and the georectification performance achieved.

MISR photogrammetric data reduction for geophysical retrievals

The theoretical concept, based on modern photogrammetric methods, underlying the design of the Multi-angle Imaging SpectroRadiometer (MISR) science data processing system, responsible for the autonomous and continuous georectification of multiangle imagery, is the subject of this paper. The algorithm partitions effort between the MISR Science Computing Facility and the Earth Observing System (EOS) Distributed Active Archive Center (DAAC) in a way that minimizes the amount of processing required at the latter location to rectify and map project remotely sensed data online, as it comes from the instrument. The algorithm deals with the following issues: (1) removal of the errors introduced by inaccurate navigation and attitude data; (2) removal of the distortions introduced by surface topography; (3) attainment of a balance between limited hardware resources, huge data volume and processing requirements, and autonomous and nonstop aspects of the production system.

Radiometric stability of the Multi-angle Imaging SpectroRadiometer (MISR) following 15 years on-orbit

The Multi-angle Imaging SpectroRadiometer (MISR) has successfully operated on the EOS/ Terra spacecraft since 1999. It consists of nine cameras pointing from nadir to 70.5° view angle with four spectral channels per camera. Specifications call for a radiometric uncertainty of 3% absolute and 1% relative to the other cameras. To accomplish this, MISR utilizes an on-board calibrator (OBC) to measure camera response changes. Once every two months the two Spectralon panels are deployed to direct solar-light into the cameras. Six photodiode sets measure the illumination level that are compared to MISR raw digital numbers, thus determining the radiometric gain coefficients used in Level 1 data processing. Although panel stability is not required, there has been little detectable change in panel reflectance, attributed to careful preflight handling techniques. The cameras themselves have degraded in radiometric response by 10% since launch, but calibration updates using the detector-based scheme has compensated for these drifts and allowed the radiance products to meet accuracy requirements. Validation using Sahara desert observations show that there has been a drift of ~1% in the reported nadir-view radiance over a decade, common to all spectral bands.

Distortion calibration of the MISR linear detectors

The multi-angle imaging spectro-radiometer (MISR) instrument, which is scheduled to fly on the EOS AM1 platform, contains nine refractive cameras (four different lens designs) at preselected view angles which image in the push broom mode. Each focal plane contains four charge coupled device (CCD) line arrays consisting of 1504 active pixels; each array is preceded by one of the MISR spectral filters. In order to facilitate registration of the data generated by the 36 arrays during the initial phase of the mission, the crosstrack pointing angle of each pixel in each array was measured in the laboratory at the camera subsystem level. These measurements were particularly challenging because the pixels had to be calibrated under flight conditions (in a vacuum over the temperature range 0 to 10 degrees Celsius) to an accuracy of 1/8 pixel or 2.6 micrometer. Given the first order properties of the various lenses, this requirement implies that the distortion had to be calibrated to better than 10 arcsec. This paper will discusses the hardware and software techniques utilized to accomplish this stringent calibration.

A simulation of EOS MISR data and geometric processing for the prototyping of the MISR ground data system

Describes a modeling system for the simulation of the Multi-angle Imaging Spectro-Radiometer (MISR) instrument push-broom data to be used in the prototyping of the MISR ground data system. The data are being simulated using the known characteristics of the instrument and spacecraft position and pointing. Rendering software obtained from the Digital Image Animation Laboratory (DIAL) at JPL has been modified to model multi-angle push-broom data. Landsat TM data are used as input radiance.<<ETX>>

Assessment of MISR Cloud Motion Vectors (CMVs) Relative to GOES and MODIS Atmospheric Motion Vectors (AMVs)

AbstractCloud motion vector (CMV) winds retrieved from the Multiangle Imaging SpectroRadiometer (MISR) instrument on the polar-orbiting Terra satellite from 2003 to 2008 are compared with collocated atmospheric motion vectors (AMVs) retrieved from Geostationary Operational Environmental Satellite (GOES) imagery over the tropics and midlatitudes and from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery near the poles. MISR imagery from multiple view angles is exploited to jointly retrieve stereoscopic cloud heights and motions, showing advantages over the AMV heights assigned by radiometric means, particularly at low heights (<3 km) that account for over 95% of MISR CMV sampling. MISR–GOES wind differences exhibit a standard deviation ranging with increasing height from 3.3 to 4.5 m s−1 for a high-quality [quality indicator (QI) ≥ 80] subset where height differences are <1.5 km. Much of the observed difference can be attributed to the less accurately retrieved component of CMV motion along the...

Airborne multiangle spectropolarimetric imager (AirMSPI) observations over California during NASA's polarimeter definition experiment (PODEX)

The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) is an ultraviolet/visible/near-infrared pushbroom camera mounted on a single-axis gimbal to acquire multiangle imagery over a ±67° along-track range. The instrument flies aboard NASA’s high-altitude ER-2 aircraft, and acquires Earth imagery with ~10 m spatial resolution across an 11- km wide swath. Radiance data are obtained in eight spectral bands (355, 380, 445, 470, 555, 660, 865, 935 nm). Dual photoelastic modulators (PEMs), achromatic quarter-wave plates, and wire-grid polarizers also enable imagery of the linear polarization Stokes components Q and U at 470, 660, and 865 nm. During January-February 2013, AirMSPI data were acquired over California as part of NASA’s Polarimeter Definition Experiment (PODEX), a field campaign designed to refine requirements for the future Aerosol-Cloud-Ecosystem (ACE) satellite mission. Observations of aerosols, low- and mid-level cloud fields, cirrus, aircraft contrails, and clear skies were obtained over the San Joaquin Valley and the Pacific Ocean during PODEX. Example radiance and polarization images are presented to illustrate some of the instrument’s capabilities.

PROBA-V geometric calibration

A system is described for the geometrical calibration of the planned PROBA-V multi spectral earth observation satellite. The largest challenge lies in the complex thermo-elastic distortion due to the absence of active thermal control onboard. The system is based on a 2 step (first by scene, then by global trend), weighted and constrained least squares inversion model. The geometric reference dataset consists in a set of automatically selected image chips from the Geocover 2000 dataset. Results show that the sub-pixel absolute localization accuracy requirements should be reached.

MISR band-to-band registration

During the standard geo-rectification processing of MISR imagery, all four spectral bands belonging to each of the nine MISR cameras are required to be geolocated and co- registered automatically to approximately one pixel accuracy. Two steps of processing are designed to accomplish this goal: (1) a complex multi-camera geolocation and co- registration of the red spectral band data for all nine cameras, and (2) the co-registration of the other three spectral bands of MISR imagery of each camera using their relationship with the already geolocated red band imagery. This paper addresses the second processing step. The geometry of the satellite orbit, the ellipsoid rotating earth, and the separation of the view angles between different spectral bands are combined in a mathematical model which describes the band-to-band line and sample parallaxes. The sensitivity study of this model to numerous error sources, such as variations in the orbit and earth radius, orbit perturbation, and navigation errors, leads to a practical polynomial band-to-band transform solution, and the decision on the usage of either a static or dynamic band-to-band transform as well as the application range of the transform.