The Submillimeter-wave and Infrared Ice Cloud Experiment (SIRICE) concept would provide global measurements of ice water path (IWP - the vertically integrated mass of ice particles per unit area), and weighted mean mass particle diameter (Dme). The SIRICE payload consists of two instruments, the Sub-millimeter/Millimeter (SM4) Radiometer, and the Infrared Cloud Ice Radiometer (IRCIR). IRCIR is a compact, low-cost, multi-spectral, wide field of view pushbroom infrared imaging radiometer. IRCIR will employ four IR sensor assemblies to produce 90° cross-track (contiguous along-track) coverage in three spectral bands with a spatial resolution of 0.6 km at nadir. Each IR sensor assembly consists of an uncooled microbolometer focal plane array (FPA), associated sensor core electronics, a stripe filter fixed at the FPA, and an IR lens assembly. A single scene mirror is used to provide two Earth view angles, as well as calibration views of space and the on-board calibration blackbody. The two Earth view angles will be used for stereo cloud height retrievals.
Si avalanche photodiode (APD) single photon counting modules (SPCMs) are used in the Geoscience Laser Altimeter
System (GLAS) on Ice, Cloud, and land Elevation Satellite (ICESat), currently in orbit measuring Earth surface
elevation and atmosphere backscattering. These SPCMs are used to measure cloud and aerosol backscattering to the
GLAS laser light at 532-nm wavelength, with quantum efficiencies of 60 to 70% and maximum count rates greater than
13 millions/s. The performance of the SPCMs has been monitored since ICESat launch on January 12, 2003. There has
been no measurable change in the quantum efficiency when comparing the average photon count rates in response to the
background light from the sunlit Earth. The linearity and the afterpulsing, seen from the cloud and surface backscattering
profiles have been the same as those during ground testing. The detector dark counts rates monitored while the
spacecraft was in the dark side of the Earth have increased linearly at about 55.5 counts/s per day due to space radiation
damage, which is a little lower than what we expected based on the ground testing and sufficiently low to provide useful
atmosphere measurements through the end of the ICESat mission. The radiation damage appeared to be slightly
dependent of the device temperature. There was also a distinct increase in the dark counts during the solar storm in 28-31
October 2003. These SPCMs have been in orbit for almost four years to date. The accumulated operating time has
reached to over 380 days (9150 hours). These SPCMs have provided unprecedented receiver sensitivity and clarity in
atmosphere backscattering measurements from space.
Micro-Pulse Lidar (MPL) systems have been utilized in a wide variety of field campaigns and are currently deployed at multiple sites around the globe to monitor atmospheric aerosols and clouds on a continuous, multi-year basis. These systems contain a commercial-grade telescope that changes focal-length as a function of instrument temperature resulting in a bias error for retrieved lidar profiles. An analytical model is described that predicts the expected thermal-induced signal response, and is used to correct MPL atmospheric data. Results demonstrate a significant reduction in data bias error.
Long-term global radiation programs, such as AERONET and BSRN, have shown success in monitoring column averaged cloud and aerosol optical properties. Little attention has been focused on global measurements of vertically resolved optical properties. Lidar systems are the preferred instrument for such measurements. However, global usage of lidar systems has not been achieved because of limits imposed by older systems that were large, expensive, and logistically difficult to use in the field. Small, eye-safe, and autonomous lidar systems are now currently available and overcome problems associated with older systems. The first such lidar to be developed is the Micro-pulse lidar System (MPL). The MPL has proven to be useful in the field because it can be automated, runs continuously (day and night), is eye-safe, can easily be transported and set up, and has a small field-of-view which removes multiple scattering concerns. We have developed successful protocols to operate and calibrate MPL systems. We have also developed a data analysis algorithm that produces data products such as cloud and aerosol layer heights, optical depths, extinction profiles, and the extinction-backscatter ratio. The algorithm minimizes the use of a priori assumptions and also produces error bars for all data products. Here we present an overview of our MPL protocols and data analysis techniques. We also discuss the ongoing construction of a global MPL network in conjunction with the AERONET program. Finally, we present some early results from the MPL network.
ISIR (Infrared Spectral Imaging Radiometer) was designed and fabricated by Space Instruments, Inc. and flown by NASA/GSFC on the Discovery shuttle mission STS-85 in August 1997. ISIR collected over 60 hours of infrared data on a variety of cloud, land, and ocean scenes. Data was obtained in four spectral bands with a single, uncooled microbolometer detector array operating in the pushbroom mode. Data was collected with varying amounts of TDI (Time Delay & Integration) to enhance system sensitivity. The design of the ISIR instrument and selected mission results will be presented.
In August 1997 an infrared spectral imaging radiometer (ISIR) based on uncooled microbolometer array technology was flown on space shuttle mission STS-85. In this paper the design of the instrument and experimental goals are presented, and initial results from the flight mission are described. The ISIR instrument provided 1/4 km resolution imagery at four wavelengths that were selected for cloud remote sensing. A major goal of the work is development of compact and less costly cloud imagers for small satellite missions. A large data set of earth imagery and test operations was obtained from the mission. In most regards the ISIR functioned within its design parameters.
This paper describes a recently completed electrooptical camera flying onboard the NASA ER-2 high altitude aircraft. The device includes a six-position filter wheel which can be fitted with a combination of polarizing and/or spectral filters. An alternate configuration will include a polarizing filter which can be rotated to any angle under computer control. The camera mount in the nose of the ER-2 can tilt forward or aft up to 40 degrees, both for bidirectional reflectance studies and for image motion compensation (the aircraft moves 34 meters between frame acquisitions). The ground resolution is nominally 5 meters from and altitude of 20 km. Spectral responsivity is that of the silicon imaging array (Kodak KAF-1400). Initial data sets were acquired in support of the International Satellite Cloud Climatology Program Regional Experiment of November, 1991, and will be used to study cirrus cloud properties.
Until a few years ago, virtually all NASA''s remote sensing was done passively. NASA is now working to develop active remote sensing systems, making use of the very rapid advances occurring in laser and radar technology. To be deployed in the difficult space environment, laser instruments must be rugged enough to withstand vibrations and cold while being able to operate automatically without retuning or realigning the instrument by hand. This paper describes several major NASA research efforts in lidar remote sensing, including hardware and key sensor issues, along with results and expectations.
A multispectral scanning radiometer has been used to obtain measurements of the reflection function of marine stratocumulus clouds at 0. 75 1 . 65 and 2. 1 6 rim. These observations were obtained from the NASA ER-2 aircraft as part of the First ISCCP [International Satellite Cloud Climatology Project] Regional Experiment (FIRE) conducted off the coast of southern California during July 1987. Multispectral images of the reflection function were used to derive the optical thickness and effective particle radius of stratiform cloud layers on four days. In addition to the radiation measurements in situ microphysical measurements were obtained from the University of Washington Convair C-131A aircraft. In this paper we compare remote sensing results with in situ observations which show a good spatial correlation for both optical thickness and effective radius. These comparisons further show systematic differences between remote sensing and in situ values with a tendency for remote sensing to overestimate the effective radius by 23 pm independent of particle radius. The optical thickness in contrast is somewhat overestimated for small optical thicknesses and underestimated for large optical thicknesses. Marginal probability density functions of optical thickness and effective radius have been derived from our remote sensing results. The joint probability density function of optical thickness and effective radius shows that the effective radius increases as the optical thickness increases for optically thin clouds in contrast to optically thick clouds for
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