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ER-2 Platform: FIRE ACE End of Mission Summary |
M.D. King, Mission Scientist
Edited By: S. Ackerman
Primary science objectives are:
The ER-2 flew 11 flights during the course of the mission. Co-ordinations with other platforms included:
ER-2 mission summaries (M. D. King - ER-2 mission scientist) and flight tracks can be found on the FIRE ACE web page. A short summary of all flights including aircraft and instrument co-ordinations, instrument performance, and cloud conditions is given in the following table. (M.D. King)
Instrument summaries follow with contributions made by S. Ackerman (HIS), M. Goodman (AMPR), D. Hlavka (CLS), R. Marchand (AirMISR), P. Pielwskie (SSFR), S. Platnick (MAS), P. Racette (MIR), and B. Smith (Satellite).
| Mission | Date | Aircraft coordination | Satellite coordination | MAS | MIR | AirMISR | AMPR | SSFR | HIS | CLS | Comments |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Transit (98-063) |
May 13 | S | S | S | S | S | S | S | Transit flight from Dryden to Fairbanks, AK | ||
| 1 (98-064) |
May 18 | C-130Q | NOAA-14 F-14 |
P | S | P | S | S | P | P | Overflight of SHEBA ice station on E-W and N-S flight tracks, coordinated with C-130Q at solar noon |
| 2 (98-065) |
May 20 | CV-580 C130Q |
NOAA-14 F-14 |
no port 4 | S | P | S | S | S | S | Clear sky near Barrow with repeated overflights of ARM site with CV-580; later overflight of SHEBA ice station and NOAA-14 ground track (Arctic stratus clouds) |
| 3 (98-066) |
May 22 | NOAA-14 F-14 |
no port 4 | S | P | S | S | S | S | Clear sky over ice and cloudy sky over tundra near Barrow; flight track coordinated with NOAA-14 ground track | |
| 4 (98-067) |
May 24 | NOAA-14 F-14 |
no port 4 | S | P | S | S | P | S | Scattered-broken cloud cover over ice and uniform arctic stratus over tundra near Barrow; flight track coordinated with NOAA-14 ground track | |
| 5 (98-068) |
May 26 | NOAA-14 F-14 |
S | S | P | S | S | S | S | Extensive cirrus over the ice | |
| 6 (98-069) |
May 27 | C-130Q | NOAA-14 F-14 |
S | S | S | S | S | S | S | Some open water along Alaska coast, with open ice and then low clouds north of the coast; extensive cloud layers over SHEBA and high thin clouds over ARM on the return |
| 7 (98-070) |
May 29 | CV-580 | NOAA-14 F-14 |
S | S | S | S | S | S | S | Extensive two-layer altocumulus/stratus clouds from Brooks Range to 74.5°N, then overlying cirrus over SHEBA; coordinatedwith CV-580 over SHEBA |
| 8 (98-073) |
June 2 | CV-580 | NOAA-14 F-14 |
S | P | S | S | S | S | S | stratocumulus clouds over ARM during CV-580 coordination; extensive altocumulus over SHEBA, clearing to north; clear sky over Barrow on return leg |
| 9 (98-074) |
June 3 | CV-580 | F-14 | S | P | S | S | - | S | S | Extensive stratus decks with 3-3.5 km tops over SHEBA during CV-580 coordination |
| 10 (98-075) |
June 4 | F-14 | S | P | - | S | S | S | P | Inhomogeneous two-layer altocumulus clouds over SHEBA with midlevel cloud tops at 4-7 km, intermittently up to 9 km | |
| 11 (98-076) |
June 6 | CV-580 | F-14 | S | S | S | S | S | S | - | Uniform stratus deck, with tops at about 0.8 km, in area of ARM site (stratus over tundra, open water, sea ice) during CV-580 coordination, some thin cirrus possible in some locations |
|
S: Successful P: Partially successful -: No data |
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The Advanced Microwave Precipitation Radiometer (AMPR) is a total power scanning multifrequency passive radiometer which collects data at 10.7, 19.35, 37.1, and 85.5 GHz. The AMPR comprises two adjacent antenna systems with one large scanning mirror accommodating both systems. One antenna system uses a copy of the SSM/I feedhorn for the three higher frequencies. The second antenna system collects data at 10.7 GHz. The ground spatial resolution of the nadir footprint is 0.6 km for the 85.5 GHz channel, 1.5 km for the 37.1 GHz channel, and 2.8 km for both the 19.35 and 10.7 GHz channels. The AMPR calibrates with external cold and warm loads after every fourth data scan. A total calibration sequence or a total data are each performed in a three-second time period. The AMPR scanner sweeps through a total 90o (+/- 45o from nadir) data scan collecting a sample for each channel every 1.8o for a total of 50 samples per channel. Based upon an aircraft altitude of 20 km and an aircraft speed of 410 knots, this scan rate will yield contiguous footprints for the 85.5 GHz channel within a 40 km wide swath. The alignment of the feedhorns has been adjusted such that vertical polarization is received 45o to the left of nadir and horizontal is received 45o to the right of nadir. An equal mixture of vertical and horizontal polarizations is received at nadir.
AMPR collected data on 11 data flights plus the two ferry flight to and from Dryden Flight Research Facility on 30 May and 1 June to repair the ER-2. In all AMPR flew successfully on a total of 14 flights. AMPR performed extremely well throughout the experiment. There were an unusually low number of bad data scans, (i.e., "noisy data" either from scan-to-scan or pixel-to-pixel) and compared to previous AMPR deployments, the occurrence of bad data scans was lower than in any other experiment.
Initial analysis of the instrument performance reveals the following:
| Channel (GHz) | Sensitivity (K/count) | delta T (RMS error) |
|---|---|---|
| 10.7 | 0.12 | 0.24 |
| 19.35 | 0.20 | 0.43 |
| 37.1 | 0.15 | 0.22 |
| 85.5 | 0.25 | 0.32 |
A more extensive assessment of the data quality will be performed during the next several months.
The deployment of the AMPR microwave radiometer provided an opportunity for the FIRE ACE science team to explore new methods for deriving cloud properties from both satellite and airborne passive microwave measurements. The complement of the AMPR (10, 19, 37, 85 GHz) with the MIR (90, 150, 183 ± 7, 220 GHz) brought to bear a broad range of microwave frequencies on the problem of separating and interpreting the microwave signals of clouds and sea ice. A high variety of sea ice, open water, and cloud conditions have been sampled. The AMPR data will be particularly useful in identifying leads, first-year ice, multi-year ice and open water. Changing ice conditions during the time of the experiment have been obtained for locations flown over repeatedly by the ER-2. A few cases of coincident data collected with other FIRE ACE passive microwave radiometers have been obtained. These coincident data will be used to test the feasibility of detecting clouds over sea ice backgrounds for future passive microwave satellite applications. With the field phase completed, additional work will now be focused on combining the satellite-based (SSM/T2, AMSU, SSM/I) and airborne radiance measurements, together with ground-based and airborne in situ measurements. Specifically, attempts will be made to develop methods for obtaining cloud liquid water path, ice water path, and precipitation rate over sea ice. Comparison of retrieved variables with in situ measurements, and comparison of the satellite algorithms with airborne retrievals to elucidate the effect of spatial resolution and intervening atmospheric attenuation will be performed with the intent of improving satellite algorithms for eventual routine use.
This was the first experiment in which AMPR was flown over sea ice. The following observations about the data reveal that AMPR:
The data collected have demonstrated great promise in identifying varying surface background features such as land, snow, water bodies, and ice features including leads, first-year ice and multi-year ice.
AMPR's FIRE ACE experiment objective involved a collaborative research between the AMPR and Microwave Imaging Radiometer instrument collocated on the ER-2. Specifically we plan to:
Figure 1. Image of the AMPR channels over the Barrow ARM site and Beaufort
Sea.
Figure 2. Flight track of the ER-2, red section highlights the AMPR imager
shown in Figure 1.
AirMISR is an airborne instrument for obtaining multi-angle imagery similar to that of the satellite-borne MISR instrument and flies on the NASA-owned ER-2 aircraft. AirMISR has a single pushbroom (line imaging) camera of the same design as the nine cameras on the MISR instrument. In each camera, images are obtained in four spectral bands. The centers wavelength of these bands are 443, 555, 670, and 865 nm with about a 10 nm bandwidth. The AirMISR camera pointing angle can be adjusted in flight (along the direction of flight) from +70.5o to -70.5o relative to nadir. By rotating at specific times, images of the same target from a variety of angles can be obtained. During this mission the camera was adjusted to reproduce the nine view angles which was obtained by the satellite (that is, nadir plus 26.1, 45.6, 60.0, and 70.5o forward and aftward of the local vertical).
During the course of this experiment, AirMISR successfully acquired data over a variety of arctic cloud conditions. Cloud types observed include both thin and thick, and high, low and multilayered clouds. Data was also acquired over land, ice, and on one occasion a large area of open water. In combination with data from other airborne instruments (esp. MAS, SSFR, and CLS) and ground-based instruments (esp. lidar, radar and downwelling radiation), this data set will provide a rich resource for members of the MISR science team to examine MISR cloud products. In particular, this data should prove valuable in testing our albedo and cloud masking algorithms and, in a few instances, in testing the stereo-matching algorithms for cloud top height retrieval.
In a real sense, this was AirMISR's first major field deployment, and it was not without some difficulties. In particular, almost all of the acquired images contain a number of dropped lines which vary from about 18% to 2%, seemingly at random, from image to image. As part of the navigational correction, drop lines will be filled in via a linear interpolation from nearby good data. AirMISR also had difficulty in achieving all pointing angles. A flight-by-flight summary of the instrument performance is given below.
Much of the raw data gathered by AirMISR has already been shipped to JPL where it will be processed and archived. The MISR team intends to provide calibrated and navigationally corrected (that is, pitch and roll adjusted) radiance data to the scientific community as soon as possible. We estimate that some of this data will become available as early as June 30, and will be accessible at the MISR home page. FIRE ACE science team members will be alerted by email as the data becomes available.
18 May (4 km target surface) C-130 flew over Sheba 2300 UTC on south-bound leg
20 May (1 km target surface) Barrow Runs Coordinated with CV-580
22 May () Nav. failure on ER-2, Mission altered mission en route to Barrow
24 May (1 km target surface) UW CV-580 failed to lift-off for planned coordination
26 May (1 km target surface) MMCR, CLS and AirMISR images suggest cirrus moving over ship (from S to N) and thickening with time. The surface is visible through the cirrus on earliest runs over the ship
27 May (8 km target surface)
29 May (3 km target surface) UW CV-580 made above and below cloud BDRF measurements at ship
2 June (3 km target surface) UW CV-580 made above and below cloud BDRF measurements at ship
3 June (3 km target surface) Flew three-leafed clover pattern.
4 June --- Failed all Runs ---
6 June (3 km target surface)
The CLS is a standard instrument for NASA ER-2 cloud remote sensing missions. The lidar functions to unambiguously define the vertical cloud structure up to the limit of optical attenuation. The CLS information is critical to the correct interpretation of data from all the passive sensors.
The CLS provides the direct truth measurement on the cloud heights, type of clouds and multiple layering. Specific objective of the CLS group for the FIRE ACE mission includes the analysis of arctic cirrus data for relative visible optical thickness and infrared emissivity. The effect and interactions with cirrus for high frequency microwave observations is also a special area of interest. The CLS group also supports the lidar instrument at the ARM site near Barrow, Alaska. The interest is in data comparisons with the surface data from the ARM site.
For the FIRE ACE mission, a new lidar measurement experiment is being attempted. The 532 nm channel of the CLS was modified so that the detector could be put into a direct signal integrate mode such that the signal may be directly interpreted as the integrated backscatter signal from the surface and clouds. Normally the surface signal is saturated and not measured. Thus, the change in surface reflectance due to change in reflectivity and cloud attenuation will be observed. In addition, a test measurement of the integrated surface signal from a field of view that was displaced from the direct nadir return by 3.5 milliradians was implemented for one flight. The off nadir signal is due to multiple scattering only, principally forward scattering within the diffraction peak. The theory is that there will be a direct relationship between the off nadir signal and the particle size for transmissive cloud layers. It is hoped that there will be in situ measurements of particle size to compare with these observations as a result of the ACE missions.
The CLS flew on 11 data flights, from 13 May 98 through 04 June 98, counting the ferry flight to Fairbanks. The instrument recorded data every flight during this period, with the system working nominally every flight but two. Several of the ER-2 flights were coordinated with the C-130 and the CV-580. In-the-field analysis included high resolution line-scan recorder strip charts, quick-look flight summary images, and course resolution cloud boundary location ascii files. The images and boundary files can be accessed from the FIRE-ACE home page. An example image is provided for May 22 flight (Figure 3).
The flights covered a wide range of cloud types covering cirrus over low stratus/fog, stratus/fog - clear sky mix, thick cirrus, complex multiple layer, and uniform stratus with no cirrus. The off-nadir signal was implemented for the flight on 03 June 98 for the 532 nm channel. Preliminary analysis of the signals from this channel show weak backscatter from multiple scattering detected both from stratus clouds and ground return. The ground return appears to be stronger than the stratus return, which was not expected. More detailed analysis will take place back at Goddard.
The CLS information is critical to the correct interpretation of data from all the passive sensors. CLS data is used extensively in MAS and HIS data analysis.
Figure 3. CLS quick look image of cloud structure along the ER-2 flight path on
May 22, 1998.
The High-Resolution Interferometer Sounder (HIS) is an instrument developed at the University of Wisconsin - Madison Space Science and Engineering Center (UW-SSEC) providing vertical resolution atmospheric temperature and moisture soundings derived from upwelling atmospheric radiation. The HIS has participated in many prominent meteorological field experiments worldwide since its birth in the mid 1980's,including FIRE I, II and now FIRE III. The HIS instrument is flown aboard NASA ER2 aircraft, mounted within a pod under the center line of the fuselage. Flight level is at approximately 20 km (65,000 ft) or 50 mb. The instrument is shock mounted to dampen high-frequency vibrations from the aircraft. The HIS instrument is based upon Michelson interferometric, generating interferograms as initial products. Interferograms are produced at the rate of one every six seconds, with twelve interferograms produced before on-board calibration is performed. The three spectral bands of the HIS cover the region from 3.8 to 16 microns at high spectral resolution.
The HIS makes accurate radiometric measurements (absolute error < 1° K) with a reproducibility of 0.1° K observing the upwelling radiance at sufficiently high resolution to identify individual absorption lines. This unique capability has resulted in the HIS measurements playing a central role in verifying and improving clear-sky, line-by-line radiative transfer models. The HIS data, in conjunction with other observations made during these experiments, provide a unique and important data set for future line-by-line models which implement cirrus clouds. HIS observations have been extensively used to develop methods of retrieving atmospheric temperature and moisture profiles. The techniques are physically based on the simultaneous retrieval of atmospheric temperature and water vapor from over 3000 HIS spectral radiance observations.
In addition to the high-spectral resolution measurements made by the HIS, ground-based interferometers (Atmospheric Emitted Radiance Interferometer - AERI) were operated continuously at the SHEBA Ice camp and ARM site in Barrows AK.
The primary objectives of the HIS program during ACE-FIRE III were:
Appropriate measurements were made to address these objectives.
The HIS instrument performed well throughout the FIRE-ACE experiment but with two exceptions. Two hours of data were collected at the beginning of the flight on May 18 due to an interferometer alignment failure. A scene mirror failed to rotate on May 29; 3.5 hours of data were collected. HIS collected data during the remaining 9 flights for nearly the entire flight time.
Analysis of HIS data collected during FIRE-ACE can be found at the SSEC/FIRE Arctic Cloud Experiment Home Page. This document presents examples from one day.
Primary HIS observations during FIRE I and II focused on ice clouds. ACE/FIRE III provided the opportunity to achieve high-spectral resolution observations over extended stratus. Many cases of stratus alone were collected during ACE/FIRE III. These scenes will be used to develop cloud property and atmospheric temperature and moisture profile retrieval algorithms.
We have observed variations in the spectral emissivity of clouds and ice. Figure 4 shows a comparison of the HIS measured brightness temperature of a stratus cloud and a clear-sky scene over ice. The only difference that occurs in brightness temperature of these two scenes is the 10-12 µm (850-1000 cm-1) spectral region and beyond 2400 cm-1.
Measurements during clear-sky conditions provide opportunities to validate and improve the modeling of radiative transfer in the atmosphere. Figure 5 compares a theoretical simulation with HIS observations. These observations were made in the vicinity of AERI observations. Thus, the calculations will be validated with simultaneous ground and high-altitude measurements.
Figure 4. A comparison of HIS observations over stratus cloud and a clear-sky
scene over ice.
Figure 5. A comparison of HIS observations near SHEBA with radiative transfer
calculations.
The Millimeter wave Imaging Radiometer (MIR) as configured for the FIRE-ACE experiment is a seven-channel scanning radiometer with channels at 89, 150, 183 ± 1, 183 ± 3, 183 ± 7, 220, and 340 GHz. The nominal antenna beamwidth for each channel is 3.5°, and the swath scanned is 100°. The 340 GHz channel is a new channel just installed in March 1998. The MIR has primarily been used for the study and development of techniques for retrieving water vapor distributions. More recent studies have focused on the application of the MIR frequencies for the measurement of clouds and the effects of clouds on the retrieval of atmospheric water vapor. The FIRE-ACE experiment is an excellent opportunity for extending the data set for such analyses.
The frequency ensemble of the MIR, along with measurements from other instrumentation, are useful for inferring surface properties, cloud coverage, and water vapor distributions. The higher frequency channels, i.e., 183 GHz and higher, are sensitive to the presence of cirrus clouds. Scattering from cloud ice is observed as depressions in brightness temperatures. Absorption by atmospheric water vapor obscures the surface. The 89 and 150 GHz channels respond to fluctuation in the surface emissivity. These channels also respond to water cloud. In dry conditions like those observed during the FIRE-ACE campaign, the 220 GHz channel also displays significant response to surface conditions and cloud absorption. The measured temperatures at these channels are a function of the surface albedo and path attenuation. The data set acquired will be used to study the scattering characteristics of ice clouds, the utility of the new 340 GHz channel and the interaction of surface characteristics and low level clouds detected in the atmospheric window channels. Another application of the MIR data set is the retrieving surface albedo and columnar water vapor in the presence of clouds over ocean ice. Finer spatial resolution of sea ice distributions may be obtained using millimeter wave frequencies than using microwave frequencies.
The MIR instrument performed well throughout the FIRE-ACE experiment with a few exceptions. There were three data flights (on days 153, 154, and 155) during which the MIR exhibited a problem with the A/D boards resulting, in about a 30% data loss.
Figure 6 shows MIR brightness temperatures from the seven-radiometric channels. The horizontal strips in the images result from the problems associated with the A/D board. The 340 GHz channel is mislabeled as 325+/-3. Cloud Lidar System data shows a thin stratus layer starting at about 23:36; a layer of moderately thick cirrus is present at 23:40 and then the stratus cloud becomes significantly thicker. Low level clouds or fog over the ice are present in the CLS data in the time preceding the stratus layer, increasing the brightness temperatures of the window channels. A clearing in the fog occurs between 23:30 and 23:35. The 89, 150 and 220 GHz channels detect this clearing, indicated by a drop in brightness temperatures. Leads in the ice can be seen in the 89 and 150 GHz channels and in some cases the 220 GHz channels.
Figure 6. MIR brightness temperature images. A clearing in low-level cloud is
observed between 23:30 and 23:35. Leads in the ice are present between 23:40
and 23:45.
The MODIS Airborne Simulator (MAS) is a scanning spectrometer with 50 meter spatial resolution at nadir, a 38 km swath width, and 50 spectral channels from the visible through the thermal infrared (0.55 - 14.3 µm). Further information can be found at the MAS web site.
MAS data taken during FIRE ACE will be used for:
Validating of the MODIS cloud mask algorithm for distinguishing clouds from snow and sea ice surfaces in the polar regions (using a variety of solar and IR tests)
Testing of MODIS cloud retrieval algorithms over sea ice surfaces during summer daytime conditions (relying heavily on the 0.86, 1.6, 2.1, and 3.7 µm MAS bands)
Comparing satellite and ground based-observations of clouds and clear sky in polar regions; comparing SHEBA and ARM long-term, ground-based remote sensing sites
Providing high spatial resolution imagery in support of other platform instruments
The MAS performed normally, with the exception of several problems with the Port 4 spectrometer (nine channels in the 8 - 14 µm TIR region.) The dewar for this detector arrived at Ft. Wainwright with a massive leak, so no TIR data were collected on the ferry flight (ER-2 sortie number 98-063, 5/13/98). The leak was repaired prior to the next flight, 98-064 (5/18/98), but channel 42 (8.6 µm) failed and the others were noisy. Band 45, for example (11.0 µm), had an NEdT (noise equivalent temperature) of 0.48 C on this flight, compared to a nominal specification of 0.10 C (King, et al 1996).
The Port 4 dewar was subsequently removed for a de-watering procedure; hence, the next three flights (98-065, 5/20 through 98-067, 5/24) were flown without these nine TIR channels. The other 41 channels functioned normally. The Port 4 dewar was re-installed for flights 98-068 (5/26/98) through 98-070 (5/29/98.) The noise in the TIR channels was improved, with Band 45 now at 0.38 C NEΔ T. (It should be noted that these numbers refer to precision, rather than accuracy).
Prior to the unscheduled return flight to NASA Dryden, some additional signal shielding was added, which resulted in a further improvement in Port 4 performance; NEΔ Ts for Band 45 were at 0.25 C for the remainder of the deployment. That this number remains higher than the MAS specification is partly due to degradation of the Port 4 Germanium window, possibly coupled with damage to the detector array caused by the vacuum failure.
All MAS flights have been processed within about 3 days of flight at NASA GSFC. Level 1B data will be sent to Langley Research Center DAAC for archival and distribution. Initial processing is being made with a preliminary pre-flight calibration. Users should be aware that post-flight and field calibration work may result in the reprocessing of the initial FIRE ACE MAS data set.
MAS documentation, ordering information, experimental data (including browse imagery for each flight), ER-2 flight tracks and mission summaries can be found at the MAS web site.
Coordinations with in situ aircraft are important for validation of MAS cloud microphysical retrievals. During the ER-2 mission, there were 5 coordinated flights with the University of Washington CV-580 (May 20, 29; June 2, 3, 6) and 3 coordinations with the NCAR C-130Q (May 18, 20, 27).
A variety of atmospheric conditions were observed during these missions including clear sky, broken low cloud, uniform stratus decks, and multi-layer clouds and cirrus. Cloudy scenes were observed over tundra, open water to the southwest of Point Barrow, and sea ice of various types, structure, and age.
Initial imagery demonstrates the strong and often confusing effect of an underlying bright sea ice surface on cloud reflectance in the visible MAS channels. This is in contrast to the corresponding dark reflectance of ice surfaces in the 1.6, 2.1, and 3.7 µm bands used by cloud retrieval algorithms. Comparisons with AMPR have allowed several complicated scenes in the MAS imagery to be interpreted as the effect of a surface transition between sea ice and open water.
SSFR (ER-2, UW CV-580, SHEBA ice station): spectral irradiance measurements in conjunction with MAS cloud retrievals for use in comparing cloudy sky energy budget calculations with models. Potential flights would be those with relatively homogeneous cloud fields.
AMPR (ER-2): sea ice versus open water retrievals needed for analysis of MAS cloud retrievals and cloud masking.
CLS (ER-2): location of cloud tops and the presence of thin cirrus needed for understanding MAS imagery, cloud masking, and cloud retrievals.
HIS (ER-2): calibration of IR channels.
NOAA-14: eight coordinations where ER-2 heading was designed to match that of the polar orbiter at the time of the satellite overpass.
Two color composite examples of MAS imagery are shown below. The first image shows a clear sky scene over the ARM site with fast ice surrounding Point Barrow and melt ponds on land; vegetation reflects strongly in the 1.6 µm band. The second image shows an overcast stratocumulus deck near the SHEBA ice station with the 1.6 and 2.1 µm reflectances bands being sensitive to cloud droplet sizes.
Figure 7. Fast Ice over Point Barrow and the NSA ARM site, 0106 UTC 3 June 1998
(color composite with Red=1.62 µm, Green=0.74 µm, Blue=0.47
µm).
Figure 8. Stratocumulus near the SHEBA ice station, 2323 UTC 18 May 1998 (color
composite with Red=2.15 µm, Green=1.62 µm, Blue=0.55 µm).
The NASA Ames Solar Spectral Flux Radiometer (SSFR) was deployed on three platforms during FIRE-ACE/SHEBA: The ER-2 during the period from May 18 to June 7; the University of Washington from May 19 to June 7 with flights continuing until June 24; and on the SHEBA ship beginning May 14 and continuing through June 24. On both aircraft, the SSFR viewed in both the zenith and nadir directions, measuring moderate resolution (5-15 nm) spectral irradiance (flux) continuously between 300 -2200 nm. On the ice surface at the SHEBA ship the SSFR was zenith pointing.
The primary mission objective of SSFR was to assess the solar radiative energy budget over the Arctic, and for this reason a full hemispheric light collector was used, as opposed to narrow-field viewing optics more suitable for cloud and surface remote sensing. Nevertheless, the SSFR data will also prove to be an important remote sensing tool as well, especially when coordinated with other data sets such as MAS, HIS, and the CLR on the ER-2, and the CAR on the CV-580. A much more complete understanding of radiative process in the Arctic is expected with the combination of these various sensors and the in situ microphysical sampling instrumentation on the CV-580. The objectives will, of course, be determined only after detailed assessment of our data quality, application of all calibration data, and implementation of navigational correction procedures for both of the aircraft platforms. Several aspects of the experiment, however, indicate that it has been an unprecedented success. Numerous coordinated flights between the ER-2 and CV-580 occurred over the Barrow ARM site and over the ice and the SHEBA ship. Nearly all types of possible atmospheric conditions were observed: clear, broken low cloud, complete stratus cover, and multi-layer clouds. Several tens of thousands of spectra from the SSFR's on the three platforms were collected. SSFR performance is also very optimistic. Initial indications are that the instruments on each of the three platforms worked well for most of the operating periods, with the following exceptions:
For each of the three platforms a field calibration device was included to monitor the stability of the SSFR over the duration of the experiment. Absolute radiometric calibrations and spectral calibrations were performed before every ER-2 flight and nearly as frequently on the CV-580. Laboratory calibrations before the mission were conducted for absolute radiometric response, wavelength response, and angular response. Identical calibrations will be applied at the conclusion of the mission. The SSFR was calibrated in the laboratory at the ER-2 Flight Sensor Facility and calibrated against the same standards used for MAS. This will prove highly beneficial when coordinating data sets from these sensors.
We have observed spectral albedos over clouds and ice in the 80-90% range. One interesting aspect from ER-2 spectra was evidence of the broad-band Chappuis ozone absorption feature in the upwelling flux, opposite from the mid-latitude cases where it is seen in the downwelling because most of the ozone there is above the flight altitude of 20 km. Other phenomenological observations, such as changing albedo due to surface type, differences due to sampling differences between the ER-2 and CV-580, and correlation with MAS, have been noted. However, most of the analysis will depend upon detailed correlation between platforms, correlation with other remote sensors, correlation with microphysics, and detailed navigational coordinate transformation procedures.
In order to improve our understanding of clouds and climate and to provide cloud and radiation fields for climate and process models, the satellite remote sensing group at NASA Langley is working to develop a globally robust, satellite-based, retrieval program to determine the microphysical and macrophysical properties of clouds and their corresponding radiative properties. This program is being tested and improved in the arctic region using FIRE ACE data.
During phase I of the FIRE ACE, a web page was created and maintained at NASA Langley for the dissemination of satellite imagery. See the SAFIRE Satellite Page Arctic Cloud Experiment. The purpose was to provide AVHRR imagery over the experiment domain in near real time to aid in forecasting and mission planning. An SGI workstation and video projector were manned in Fairbanks to aid in mission planning meetings. Additionally, orbital predictions for all the appropriate meteorological satellites were provided. An archive of the AVHRR imagery collected during the experiment is available in GIF format at this site. The radiance data is in McIDAS format and will be forwarded to the NASA Langley DAAC. A summary of the AVHRR data collected during the experiment is depicted in Figure 11. An attempt is being made to identify any missing data and to retrieve that data from NOAA's Satellite Active Archive. A listing of satellite overpasses during the aircraft missions as well as satellite imagery with flight track overlays is available on FIRE.ACE Satellite Measurements page.
Several algorithms are being applied to the AVHRR data to derive cloud and radiation parameters. Comparisons with surface and aircraft data will aid in estimating the uncertainties in the satellite retrievals and to improve the algorithms. An incomplete list of potential collaborations includes:
Comparison of AVHRR-derived cloud boundaries with surface-based lidar and radar on the ship and at Barrow and with the ER-2 cloud lidar (CLS).
Comparison of AVHRR-derived broadband shortwave and longwave fluxes with estimates from broadband sensors flown on the C-130 and ER-2.
Comparison of AVHRR-derived cloud microphysical parameters (re, iwp(lwp), phase) with microphysical measurements deduced from in-situ probes flown on the C-130.
Comparison of AVHRR-derived cloud parameters with parameters derived from passive remote sensing instruments (Air-MISR, HIS, MAS, MIR, SSFR...) flown on the C-130 and ER-2.
