The experiment summary report is available in PDF format (615 KB). Below is an abbreviated summary.
On June 29 and 30, 1999, the ER-2 flew various flight lines, and acquired AirMISR and MODIS Airborne Simulator (MAS) images. These data will be used by the MISR science team to validate aerosol retrieval techniques by comparing results from the AirMISR data with those derived from the surface-based observations. Graham Stevens, of the CloudSat team, will make use of the MAS data to validate cloud-height and optical depth retrieval algorithms.
Originally the gathering of aircraft and ground instrumentation was made in order to support cloud bi-directional reflectance factor (BRF) studies (see Cloud Study Objectives, below). Two Twin Otter aircraft provided the opportunity to acquire radar profiles through the clouds, as well as acquire aerosol size and composition information with altitude by making use of in-situ aircraft samplers. A ground radar station based 30 feet from the shore was supplied by Roger Marchand of Penn State University. This site was supplemented by JPL sunphotometer instruments. An unlikely number of clear sky days, combined with high winds at Dryden on days where cloud conditions were appropriate, prevented the primary objectives from being fully met. However, we believe the data sets which were acquired are highly valuable scientifically, particularly for clear-sky aerosol retrieval studies.
On June 29th the ER-2 flew over a target point intersected by the Marina off-shore canyon (running East/ West) and the future Terra ground track some 12 miles from the shore. Two passes were made, one along the Terra ground track, and the other perpendicular to this path. This azimuthal sampling scheme was repeated two additional times this day and the next. Skies were clear during the offshore data acquisition, and partly cloudy during the next two runs over the ground radar/ sunphotometer site. A fifth run was make on June 29th, over a cloud deck.
The second day of the experiment was done in support of CloudSat validation team objectives. Data were acquired in conjunction with the UARS Oxygen A sensor, which was turned on for this experiment. Two runs were acquired over a cloud deck, and two over the radar site.
Additional data sets are available from ocean buoys, as well as AVHRR data.
Contact the MISR validation team for further information.
We wish to thank Roger Marchand, and Graeme Stephens for organizing this experiment.
AVHRR albedo and SST (thermal) channel images bracketing the flight
GOES vis images every 15 minutes covering flight time
TOMS Aerosol Index (global, once daily)
AVHRR Aerosol Optical Depth (global, once daily)
Buoy Readouts (surf wind speed, direction, temperature, pressure at 3 fixed locations)
AERONET aerosol optical depth at 4 wavelengths (actual source: our Mark Helmlinger)
MAS (MODIS Airborne Simulator) thumbnail images covering the flight time (I've requested the digital data)
Navy Global Visibility maps and aerosol loading maps (not useful for our palce and time)
NOAA Back Trajectory Runs, showing, according to a model, where the air at different elevations had been every 6 hours for the previous 5 days.
The primary purpose of this experiment is to examine variations in the cloud structure and their effect on the scattered radiances and MISR (the Multi-angle Imaging SpectroRadiometer) retrievals of cloud albedo. The MISR instrument (which is scheduled for launch in summer of 1998 on board the EOS-AM1 platform) makes high resolution images in four narrow spectral bands located at 443, 555, 670, and 865 nm and at nine zenith view angles 0, ±26.1, ±45.6, ±60.0, and ±70.5 degrees relative to nadir.
Data collected at the nine angles when combined with models for the cloud bi-directional reflectance distribution function (BRDF) can be used to estimate cloud albedo. That is, the nine radiance measurements are used to estimate the scattered radiance in all other directions. The cloud BRDFs used by MISR have been developed using monte carlo scattering codes and have built into them varying amounts of cloud heterogeneity. The current MISR algorithm selects a particular BRDF model based on both the variability of the cloud radiances at the several pixel scale (about 2.2 km) and based on the nine angular radiance measurements for each image pixel. In this mission, multiple pass measurements over single layer marine stratus clouds will be made on several days using AirMISR. AirMISR is an airborne instrument for obtaining multi-angle imagery similar to that of MISR. AirMISR flies on the NASA-owned ER-2 aircraft and has a single pushbroom (line imagining) camera of the same design as the nine cameras on the MISR instrument. The AirMISR camera pointing angle can be adjusted in flight from +70.5 o to -70.5 o relative to nadir along the direction of flight. By rotating the camera at specific times, images of the same target from a variety of angles can be obtained.
The AirMISR image resolution is approximately 7 meters at nadir and 21 meters at 70.5 o , which is higher than that of the MISR instrument. This will permit examination of variations in the radiance field on spatial scales which are below the MISR resolution. Also, by making measurements in several azimuth planes, we can directly evaluate the model BRDF to the degree the cloud field does not change appreciably between overflights.
Currently MISR plans call for a set of four narrowband albedos to be produced routinely. However, it is recognized that there will be strong interest from the scientific community in having broadband albedos. Thus the addition of MAS (the MODIS airborne simulator) with its wide spectral coverage will be included to study this issue. MAS also has a wider field of view than AirMISR which is useful in evaluating the homogeneity of the cloud field outside the AirMISR image area. It is also possible that the solar spectral flux radiometer (SSFR) will be included.
In addition to the above, we plan to take advantage of several other measurements being made as part of an experiment being organized by Dr. Bruce Albrecht at the University of Miami. In particular, Albrecht and his associates will have (1) two Twin Otter aircraft (one making in-situ measurements of both cloud particles and turbulence and the other with a downward or sideways looking millimeter cloud radar), (2) a ground-based scanning millimeter cloud radar, and (3) several passive radiometric measurements. This last category includes estimates of liquid water path from the Penn State microwave radiometer which Roger Marchand will deploy.