NPOESS instruments continue their missions

Scheduled for launch in October 2011, NPP (above) is designed to provide continuity with NASA's Earth Observing System (EOS) satellites for climate observations and to provide the operational weather community with risk reduction for the next generation of weather satellites. An identical satellite called JPSS-1 was ordered in September 2010 for launch in 2014. (NOAA graphic)

Initiated in 1994, the National Polar-Orbiting Operational Environmental Satellite System (NPOESS) was planned to be this country's next-generation satellite system for monitoring weather, atmosphere, oceans, land, and the near-space environment. The launch date was expected to be 2013, with the first NPOESS satellite carrying a host of sophisticated sensors and other equipment.

It was intended that the National Oceanic and Atmospheric Administration (NOAA), National Aeronautics and Space Administration (NASA), and the Department of Defense (DOD) would collaborate to build one satellite system to gather this data.

However, after numerous cost overruns and delays in development over the years, the White House decided to restructure the program in February 2010. Now, instead of a tri-agency approach, "NOAA and NASA have teamed up to develop the Joint Polar Satellite System (JPSS), which will handle the afternoon polar orbit, and DOD will create the Defense Weather Satellite System (DWSS) to cover the early morning orbit," says John Leslie, communications spokesperson for NOAA. (The European Organization for the Exploitation of Meteorological Satellites will continue to provide the U.S. with mid-morning data from its MetOp satellites.)

JPSS-1, the first satellite, is being readied for a 2014 launch. The on-board instruments for capturing the high-resolution data needed to monitor Earth's changing climate will be the same as the instruments originally planned for NPOESS -- the Visible Infrared Imager Radiometer Suite (VIIRS), Ozone Mapping and Profiler Suite (OMPS), Cross-Track Infrared Sounder (CrIS), Clouds and the Earth's Radiant Energy System (CERES), and Advanced Technology Microwave Sounder (ATMS).

Visible/Infrared Imager Radiometer Suite (VIIRS)


The Visible Infrared Imager Radiometer Suite (Photo: Raytheon)

Built by Raytheon's Space and Airborne Systems Division, VIIRS will collect information about atmospheric cloud conditions, Earth's radiation budget (how much energy the Earth receives from the sun and how much the Earth radiates back to outer space as invisible light), clear-air land/water surfaces, sea-surface temperature, ocean color, and low-light visible imagery.

VIIRS is equipped with multi-band imaging capabilities to support the acquisition of high-resolution atmospheric imagery. "VIIRS will operate in 22 spectral bands ranging in wavelength from about 0.4 microns to 12 microns," says Jeff Puschell, VIIRS's chief scientist. "It also has a radiometrically calibrated low-light level band that will provide nearly constant 0.7 km spatial resolution visible wavelength imagery-day and night-across the entire 3000 km VIIRS swath width. Compared to current operational assets, VIIRS offers four times better spectral coverage and three times better spatial resolution at end of scan, enabling sharper resolution over a greater area. VIIRS uses an innovative spatial sampling approach to produce much sharper imagery across the entire swath out to nadir angles of more than 58 degrees."

"These sensors have been dramatically improved compared to previous operational assets," adds Karen St. Germain, acting JPSS program scientist. "It's like going from a black-and-white TV screen to high-definition color. And the highly sensitive day/night band can 'see' on the dark side of earth, using very little light reflection from the moon."

Ozone Mapping and Profiler Suite (OMPS)

OMPS will continue the long-term mission of continuously recording ozone measurements from space. These global data products will be similar to those from the Solar Backscatter Ultraviolet Radiometer and the Total Ozone Mapping Spectrometer, but with JPSS-2 (2018 launch) will have much higher fidelity from the new high vertical resolution limb profile data.

OMPS is designed to significantly outperform its predecessors. Built by Ball Aerospace and Technologies, the contractor that is also providing the JPSS platform, OMPS incorporates an advanced nadir-viewing sensor and a highly innovative limb-viewing sensor to monitor changes in the earth's stratospheric ozone.

Measurements from the nadir sensor are used to generate total column ozone measurements, with better than 50 x 50 km resolution at nadir; limb-sensor measurements generate ozone profiles of the along-track limb scattered solar radiance with 1-km vertical sampling. Both sensors will maintain long-term data product stability through periodic solar irradiance measurements.

Cross-Track Infrared Sounder (CrIS)

This hyperspectral instrument designed by ITT Geospatial Systems will provide forecasters with the most advanced atmospheric measurements possible. "The higher-resolution measurements for temperature, pressure, and humidity will be tremendously valuable for real-time weather prediction," says St. Germain.

CrIS employs a Michelson interferometer to provide high-resolution infrared spectra of the earth's upwelling radiation. It provides 1305 spectral channels covering the range from 4.6 to 15.4 microns, with a spectral resolution as fine as 0.625 wavenumbers. Advanced mercury-cadmium-telluride focal plane arrays (FPAs) provide a 3 x 3 array of 14-km pixels, which cover a 2200-km wide swath across the earth every eight seconds. The FPAs are cooled passively to temperatures as low as 81K for maximum sensitivity. CrIS includes onboard radiometric and spectral calibration sources to improve its measurement accuracy.

"CrIS will be a vast improvement over the prior generation of NOAA operational sounders in terms of a much larger number of spectral channels (1305 versus 20) and radiometric accuracy," indicates Rob Mitrevski, ITT Geospatial Systems' vice president and general manager for intelligence, surveillance, and reconnaissance systems. "It will perform similarly to NASA's Atmospheric Infrared Sounder, which has proven the value of hyperspectral sounders for meteorological forecasting."

Clouds and Earth Radiant Energy System (CERES)

After more than a decade in orbit, the Clouds and the Earth's Radiant Energy System (CERES) continues to transmit data on both solar-reflected and Earth-emitted radiation from the top of the atmosphere to the Earth's surface. CERES data is used to better understand the role of clouds and the energy cycle in global climate change.

CERES utilizes three sensor assemblies with cassegrain optics and thermistor bolometer detectors. Sensors measure thermal radiation in the near-visible through far-infrared spectral region. Each scanner has three channels: a shortwave channel measures reflected sunlight (0.3 to 5 microns) to 1 percent accuracy; a longwave channel measures earth-emitted radiation (8 to 12 microns) to 0.3 percent accuracy; and a total channel (0.3 to >50 microns) accurate to 0.5 percent. The sensor channels are coaligned and mounted on a spindle which rotates about the elevation axis.

The final CERES instrument, Model 6, will fly on JPSS-1. After that an improved version of CERES, which will be called the Earth Radiation Budget Sensor (ERBS), will be built for JPSS-2. Northrop Grumman will deliver this newest sensor to NASA in 2012.

Advanced Technology Microwave Sounder (ATMS)

ATMS is a next-generation satellite microwave instrument that sees through clouds to measure atmospheric temperature, moisture, and pressure at various altitudes of the atmosphere. "The biggest change in technology compared to previous ATMS models is that we can now make measurements with one instrument instead of three," says Gary Davis, acting JPSS project manager. "The enhanced calibration fidelity delivers longer-term stability, which is ideal for identifying trends in climate change over the longer-term record."

Designed by Northrop Grumman Electronic Systems, the JPSS-1 ATMS instrument incorporates InP foundry process, low noise amplifier monolithic microwave integrated circuits (nine unique designs), and K, Ka, W and V-band receiver modules. The unit also includes radio frequency front-end modules, which enable the ATMS to cover broader microwave frequencies (23 to 183 Ghz across 22 channels).

DWSS and Beyond

The DWSS satellites will feature three instrument packages: VIIRS, the Space Environmental Monitoring (SEM) sensor, and a microwave sensor. SEM provides data on "space weather" -- charged particles that may have harmful effects on communications, navigation, and satellite and aircraft operation. DWSS will be equipped with the latest visible/IR, microwave, and space-weather sensors to provide improved spatial and spectral resolution, rapid data delivery, and increased mission life. Enhanced Department of Defense operational capabilities include being able to discriminate clouds from dust to support air operations, for example.

The type of microwave sensor DWSS will carry has yet to be determined. The microwave instrument will measure soil moisture, atmospheric temperatures, moisture profiles, precipitation, and sea-surface winds. These measurements are used for weather modeling and prediction and, combined with VIIRS imagery data, allow ground forces to plan maneuvers more safely and effectively.

Northrop Grumman Aerospace Systems is responsible for developing the satellite platform and managing instrument subcontractors and overall system integration. The first JPSS spacecraft will launch from Vandenberg Air Force Base in Santa Barbara County, California, sometime in 2014; the second satellite launch is planned for 2018.

Mark Crawford is a science writer based in Madison, Wisconsin.