ER-2 - AFRC

The Multiangle SpectroPolarimetric Imager, or AirMSPI, was a candidate for the multi-directional, multi-wavelength, high-accuracy polarization imager identified by the National Research Council's Earth Sciences Decadal Survey as one component of the notional Aerosol-Cloud-Ecosystem, or ACE, mission. The ACE spacecraft was planned to characterize the role of aerosols in climate forcing, especially their impact on precipitation and cloud formation. Forcing is the process by which natural mechanisms or human activities alter the global energy balance and “force” the climate to change. The unresolved effects of aerosols on clouds are among the greatest uncertainties in predicting global climate change. AirMSPI is conceptually similar to JPL’s Multiangle Imaging SpectroRadiometer, or MISR, carried on NASA’s EOS Terra spacecraft, but with some important additions. The new camera design extends the spectral range to the ultraviolet and shortwave infrared (from 446–866 nm to 355–2130 nm), increases the image swath (from 360 km to 680 km) to achieve more rapid global coverage (from 9 days to 4 days), and adds high-accuracy polarimetry in selected spectral bands. Like MISR, a suite of AirMSPI cameras would view Earth at a variety of angles, with an intrinsic pixel size of a few hundred meters, which for certain channels would be averaged up to about 1 kilometer.
An advanced version of this instrument is currently in development, called AirMSPI-2.

The Airborne Multi-angle Imaging SpectroRadiometer (AirMISR) is an airborne instrument for obtaining multi-angle imagery similar to that of the satellite-borne Multi-angle Imaging SpectroRadiometer (MISR) instrument, which is designed to contribute to studies of the Earth's ecology and climate. AirMISR flies on the NASA ER-2 aircraft. The Jet Propulsion Laboratory in Pasadena, California built the instrument for NASA.

Unlike the spaceborne MISR instrument, which has nine cameras oriented at various angles, AirMISR utilizes a single camera in a pivoting gimbal mount. A data run by the ER-2 aircraft is divided into nine segments, each with the camera positioned to a MISR look angle. The gimbal rotates between successive segments, such that each segment acquires data over the same area on the ground as the previous segment. This process is repeated until all nine angles of the target area are collected. The swath width, which varies from 11 km in the nadir to 32 km at the most oblique angle, is governed by the camera's instantaneous field-of-view of 7 meters cross-track x 6 meters along-track in the nadir view and 21 meters x 55 meters at the most oblique angle. The along-track image length at each angle is dictated by the timing required to obtain overlap imagery at all angles, and varies from about 9 km in the nadir to 26 km at the most oblique angle. Thus, the nadir image dictates the area of overlap that is obtained from all nine angles. A complete flight run takes approximately 13 minutes.

The NASA Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) has been in operation since 1989 acquiring contiguous spectral measurements between 380 and 2510 nm for use by a range of terrestrial ecology science investigations related to: (1) pattern and spatial distribution of ecosystems and their components, (2) ecosystem function, physiology and seasonal activity, (3) biogeochemical cycles, (3) changes in disturbance activity, and (4) ecosystems and human health. While AVIRIS continue to make unique and significant science contributions, such as its deployment to the Gulf of Louisiana in May 2010 for the assessment of the amount of oil spilled by the offshore well, the need for a new sensor to share AVIRIS’ workload and to eventually replace AVIRIS is inevitable. Indeed, since the late summer of 2009 a new NASA Earth Science airborne sensor called the Next Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRISng) is being developed by JPL through the funding support from the American Recovery and Reinvestment Act (ARRA). The technical and programmatic oversights of the AVIRISng development is provided by NASA’s Earth Science Technology Office (ESTO).

Similar to its predecessor, the AVIRIS-NG is being designed to be compatible with a broad array of possible aircraft platforms, such as NASA’s ER-2 jet, the Twin Otter turboprop, B200 King Air, and NASA’s Gulfstream III and V.

AVIRIS is the second in a series of imaging spectrometer instruments developed at the Jet Propulsion Laboratory (JPL) for earth remote sensing. It is a unique optical sensor that delivers calibrated images of the upwelling spectral radiance in 224 contiguous spectral channels (bands) with wavelengths from 380 to 2510 nanometers. It uses scanning optics and four spectrometers to image a 677 pixel swath simultaneously in all 224 bands. AVIRIS has flown in North America, Europe, and portions of South America.

The AVIRIS sensor collects data that can be used for characterization of the Earth's surface and atmosphere from geometrically coherent spectroradiometric measurements. This data can be applied to studies in the fields of oceanography, environmental science, snow hydrology, geology, volcanology, soil and land management, atmospheric and aerosol studies, agriculture, and limnology. Applications under development include the assessment and monitoring of environmental hazards such as toxic waste, oil spills, and land/air/water pollution. With proper calibration and correction for atmospheric effects, the measurements can be converted to ground reflectance data which can then be used for quantitative characterization of surface features.

ATLAS uses a tunable laser to detect an infrared-active target gas such as N2O, methane, carbon monoxide, or ozone. The laser source is tuned to an individual roto-vibrational line in an infrared absorption band of the target gas, and is frequency modulated at 2 kHz. The instrument detects the infrared target gas by measuring the fractional absorption of the infrared beam from the tunable diode laser as it traverses a multipass White cell containing an atmospheric sample at ambient pressure.

Synchronous detection of the resultant amplitude modulation at 2kHz and 4kHz yields the first and second harmonics of the generally weak absorption feature with high sensitivity (DI/I 1E-5). Part of the main beam is split off through a short cell containing a known amount of the target gas to a reference detector. The reference first harmonic signal is used to lock the laser frequency to the absorption line center, while the second harmonic signal is used to derive the calibration factor needed to convert the measurement beam second harmonic amplitude into absolute gas concentration. A zero beam is included to correct for background gas absorption occurring outside the multipass cell. The response time of the instrument is set by the gas flow rate through the White cell, which is normally adjusted to give a new sample every second. Periodic standard additions of the target gas are injected into the sample stream as a second method to calibrate the measurement technique and as an overall instrument diagnostic.

The APS is a passive sensor designed to gather high altitude dust particles for laboratory research. An APS paddle is deployed from a wingtip pod into stratosphere once the ER-2 has reached cruising altitude, and is retracted before descent. Both wire impactor and oil-film paddles are used. After approximately 40 hours of exposure, the sealed units are returned to the investigator for examination by an electron microscope. The returned particles can be the by-products of meteor decomposition in the upper atmosphere, or the products of massive volcanic eruptions.

The AOCI is a high altitude multispectral scanner built by Daedalus Enterprises, designed for oceanographic remote sensing. It provides 10-bit digitization of eight bands in the visible/near-infrared region of the spectrum, plus two 8-bit bands in the near and thermal infrared.

The Autonomous Modular Sensor (AMS) is an airborne scanning spectrometer that acquires high spatial resolution imagery of the Earth's features from its vantage point on-board low and medium altitude research aircraft. Data acquired by AMS is helping to define, develop, and test algorithms for use in a variety of scientific programs that emphasize the use of remotely sensed data to monitor variation in environmental conditions, assess global change, and respond to natural disasters.

*Note, this instrument is now on interagency loan to the USDA Forest Service

The AMPR is a total power passive microwave radiometer producing calibrated brightness temperatures (TB) at 10.7, 19.35, 37.1, and 85.5 GHz. These frequencies are sensitive to the emission and scattering of precipitation-size ice, liquid water, and water vapor. The AMPR performs a 90º cross-track data scan perpendicular to the direction of aircraft motion. It processes a linear polarization feed with full vertical polarization at -45º and full horizontal polarization at +45º, with the polarization across the scan mixed as a function of sin2, giving an equal V-H mixture at 0º (aircraft nadir). A full calibration is made every fifth scan using hot and cold blackbodies. From a typical ER-2 flight altitude of ~20 km, surface footprint sizes range from 640 m (85.5 GHz) to 2.8 km (10.7 GHz). All four channels share a common measurement grid with collocated footprint centers, resulting in over-sampling of the low frequency channels with respect to 85.5 GHz.