Minimize Aqua

Aqua Mission (EOS/PM-1)

The Aqua mission is a part of the NASA's international Earth Observing System (EOS). Aqua was formerly named EOS/PM-1, signifying its afternoon equatorial crossing time. NASA renamed the EOS/PM-1 satellite to Aqua on Oct. 18, 1999. The Aqua mission is part of NASA's ESE (Earth Science Enterprise) program. 1) 2) 3)

The focus of the Aqua mission is the multi-disciplinary study of the Earth's water cycle, including the interrelated processes (atmosphere, oceans, and land surface) and their relationship to Earth system changes. The data sets of Aqua provide information on cloud formation, precipitation, and radiative properties, air-sea fluxes of energy, carbon, and moisture (AIRS, AMSU, AMSR-E, HSB, CERES, MODIS); and sea ice concentrations and extents (AMSR-E).


Figure 1: Illustration of the Aqua satellite (image credit: NASA)


The Aqua spacecraft is based on TRW's modular, standardized AB1200 bus design (also referred to as T-330 platform) with common subsystems (Note: Northrop Grumman purchased TRW in Dec. 2002). The satellite dimensions are: 2.68 m x 2.47 m x 6.49 m (stowed) and 4.81 m x 16.70 m x 8.04 m (deployed). Aqua is three-axis stabilized, with a total mass of 2,934 kg at launch, S/C mass of 1,750 kg, payload mass =1,082 kg, propellant mass = 102 kg; power = 4.86 kW (EOL). Propulsion: hydrazine blow-down system; 4 pairs of thrusters. The design life is six years.


Figure 2: The Aqua spacecraft in launch preparation at VAFB (image credit: NASA)

RF communications: X-band, S-band (TDRSS and Deep Space Network/Ground Network compatible). All communications are based on CCSDS protocols. Like the Terra mission, Aqua provides various means of payload data downlinks, among them Direct Broadcast (DB).

Orbit: Sun-synchronous circular orbit, altitude = 705 km (nominal), inclination = 98.2º, local equator crossing at 13:30 (1:30 PM) on ascending node, period = 98.8 minutes, the repeat cycle is 16 days (233 orbits).

The Aqua spacecraft is part of the “A-train” (Aqua in the lead and Aura at the tail, the nominal separation between Aqua and Aura is about 15 minutes) or “afternoon constellation” (a loose formation flight which started sometime after the Aura launch July 15, 2004). The objective is to coordinate observations and to provide a coincident set of data on aerosol and cloud properties, radiative fluxes and atmospheric state essential for accurate quantification of aerosol and cloud radiative effects.

The PARASOL spacecraft of CNES (launch on Dec. 18, 2004) is part of the A-train as of February 2005. The OCO mission (launch in 2009) will be the newest member of the A-train. Once completed, the A-train will be led by OCO, followed by Aqua, then CloudSat, CALIPSO, PARASOL, and, in the rear, Aura. 4)

Note: The OCO (Orbiting Carbon Observatory) spacecraft experienced a launch failure on Feb. 24, 2009 - hence, it is not part of the A-train.


Figure 3: Illustration of Aqua in the A-train (image credit: NASA)

Launch: The Aqua spacecraft was launched on May 4, 2002 with a Delta-2 7920-10L vehicle from VAFB, CA. Aqua is the second satellite in NASA's series of EOS spacecraft. - Aura, the third of the three large satellites in the EOS series, was launched in July 2004 and is lined up behind Aqua, in the same orbit.



Mission status:

• Feb. 2014: The Great Lakes Region of North America is experiencing a bitter cold winter. The true color image of Figure 4 shows the mostly frozen state of the Great Lakes on Feb. 19, 2014. On that date, ice spanned 80.3% of the lakes, according to NOAA's Great Lakes Environmental Research Laboratory in Ann Arbor, Michigan. 5)

The ice reached an even greater extent on Feb. 13, when it covered about 88% of the Great Lakes – coverage not achieved since 1994, when ice spanned over 90 %. In addition to this year, ice has covered more than 80% of the lakes in only five other years since 1973. The average annual maximum ice extent in that time period is just over 50%. The smallest maximum ice cover occurred in 2002, when only 9.5% of the lakes froze over.


Figure 4: This image, acquired with MODIS on the Aqua satellite, shows the Great Lakes on Feb. 19, 2014, when ice covered 80.3% of the lakes (image credit: Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team, NASA)

• The Aqua spacecraft and its payload (except for AMSR-E which operates in a reduced mode) are operating nominally in 2014.


Figure 5: The Aqua satellite acquired this natural-color satellite image of a plankton bloom on Dec. 30, 2013. The eddy is centered about 600 km off the coast of Australia in the southeastern Indian Ocean (image credit: NASA Earth Observatory) 6)

Legend to Figure 5: In this Aqua/MODIS image, an eddy is outlined by a milky green phytoplankton bloom. Eddies are masses of water that typically spin off of larger currents and rotate in whirlpool-like fashion. They can stretch for hundreds of kilometers and last for months.

While the northern latitudes are bathed in the dull colors and light of mid-winter, the waters of the southern hemisphere are alive with mid-summer blooms. The eddy is centered at roughly 40º South latitude and 120º East longitude, about 600 km off the coast of Australia in the southeastern Indian Ocean.

• Nov. 8, 2013: The typhoon Haiyan was located over the central Philippines and was quickly heading towards the west at 22 knots (25 mph) when Aqua observed the region. 7)


Figure 6: AIRS image of the super typhoon Haiyan acquired on Nov. 8, 2013 at 04:59 UTC (image credit: NASA/JPL)

Legend to Figure 6: The lowest temperatures, in dark purple, are associated with the high, cold cloud tops of powerful thunderstorms with heavy rainfall potential. The Philippine islands stretch from the center of the image to the northwest. Northern Indonesia is at the bottom of the image, and northeastern Malaysia is at the lower left of the image. Some of the Philippine regions being pounded by the storm, in the area with purple coloring, are the Visayas, Bicol, National Capital, Central Luzon, Calabarzon, Northern Mindanao, and Mimaropa regions.

• June 2013: The 2013 Senior Review evaluated 13 NASA satellite missions in extended operations: ACRIMSAT, Aqua, Aura, CALIPSO, CloudSat, EO-1, GRACE, Jason-1, OSTM, QuikSCAT, SORCE, Terra, and TRMM. The Senior Review was tasked with reviewing proposals submitted by each mission team for extended operations and funding for FY14-FY15, and FY16-FY17. Since CloudSat, GRACE, QuikSCAT and SORCE have shown evidence of aging issues, they received baseline funding for extension through 2015. 8)

- The Aqua mission is now 5 years into its extended mission of producing a wide array of measurements in support of addressing NASA’s Earth Science mission both from the perspective of creating climate data records necessary to evaluate climate change and from the perspective of products needed to better understand fundamental Earth science processes. The Aqua mission has been extremely successful and produces a large number of critical products that are very widely used by scientists, government agencies and operational groups.

- The AMSR-E instrument, which suffered a major anomaly in 2011, now operates in a reduced mode that provides data for cross-calibration with other AMSR instruments. All other instruments on Aqua are still operating nominally and the spacecraft is in excellent health and has enough fuel to operate through 2022.

- Of the Aqua sensor complement, MODIS and AIRS are making extremely unique and popular measurements for science and operational applications. The continuity of these data products is highly desirable for the scientific community and the broader user community.

• In February 2013, Aqua is over four and a half years beyond its prime mission, and yet the spacecraft and four of its instruments continue to operate well. HSB (from Brazil) failed in February 2003, and AMSR-E (from Japan) ceased science operations much more recently, in October 2011. As of December 2012, AMSR-E is again turned on, but at a much slower rotation rate (2 rpm versus 40 rpm) than desired for science data. The AMSR-E data being collected now are largely intended for cross-calibration with data from the AMSR-2 instrument (launch on May 17, 2012) flown on Japan's GCOM-W (= Shizuku) mission. The MODIS, AIRS, CERES, and AMSU (all from the U.S.) instruments on Aqua continue to work well. It's projected that the mission could continue until 2022. 9)

The retrieved atmospheric parameters using the observations from AMSR-E on Aqua are used primarily in climate research as well as in atmospheric models used in weather forecasting. This JAXA instrument performed exceptionally well for more than three times its design lifetime. 10)

• In mid-August 2012, an intense wildfire broke out on the Greek island of Chios, sending a thick plume of smoke southward toward the island of Crete. 11)


Figure 7: MODIS on Aqua captured this natural-color image on August 18, 2012 (image credit: NASA)

Legend to Figure 7: The image shows part of the Aegean Sea dotted with many Greek islands between the mainlands of Greece and Turkey. Greece typically sees little rain between April and September and experiences some of its highest temperatures in late July and early August. Wildfires are fairly common in the hot, dry days of August.

• July 2012: Aqua is operational and has now exceeded 10 years of on-orbit operations. It has collected a wealth of data that have been used for a variety of scientific and practical purposes. Well over 2,000 scientific papers have been published using Aqua data. An example of the many Aqua results deals with the the global energy budget. 12)


Figure 8: Outgoing longwave radiation, March 18, 2011, as derived from Aqua CERES data (image credit: Tak Wong and the CERES Science Team)

Legend to Figure 8: CERES measurements allow the derivation of the solar radiation reflected from the Earth/atmosphere system back to space and the Earth’s longwave radiation emitted to space. The CERES data from Aqua and Terra have been used with incoming solar radiation data from the TIM (Total Irradiance Monitor) on the SORCE (Solar Radiation and Climate Experiment) mission to calculate that the Earth has been accumulating energy at a rate of approximately 0.50 ± 0.43 Wm-2 over the course of the 10 year period 2001-2010. 13) This slight imbalance at the top of the atmosphere means that more energy is entering than leaving the Earth system, resulting in overall warming.

• In May 2012, Aqua marked its 10th year on-orbit, delivering unprecedented data about the Earth's climate, water cycle and much more. The mission demonstrates the considerable benefits of long-term, space-based environmental monitoring. 14) 15) 16)


Figure 9: Image of stratocumulus clouds over the Pacific Ocean observed by MODIS on June 20, 2012 (image credit: NASA) 17)

Legend to Figure 9: A layer of stratocumulus clouds over the Pacific Ocean served as the backdrop for this rainbow-like optical phenomenon known as a glory. Glories generally appear as concentric rings of color in front of mist or fog. They form when water droplets within clouds scatter sunlight back toward a source of illumination (in this case the Sun). - Although glories may look similar to rainbows, the way light is scattered to produce them is different. Rainbows are formed by refraction and reflection; glories are formed by backward diffraction. The most vivid glories form when an observer looks down on thin clouds with droplets that are between 10 -30 µm in diameter. The brightest and most colorful glories also form when droplets are roughly the same size.

Another notable feature in this image are the swirling von Karman vortices that are visible to the right of the glory. The alternating double row of vortices form in the wake of an obstacle, in this instance the eastern Pacific island of Guadalupe, located ~ 240 km off the west coast of Mexico's Baja California peninsula.

• In early 2012, the Aqua spacecraft and its instruments (AIRS, AMSU, CERES and MODIS) are in nominal operation. - In June 2011, the NASA Earth Science Senior Review recommended an extension of the Aqua mission to 2015. 18)

The AMSR-E instrument operations ended on October 4, 2011. The AMSR-E instrument of JAXA (built by Mitsubishi Electric Company) continued its operation for more than 9 years (design life of 3 years). However, since the end of August, 2011, a continuous increase of relatively large antenna rotation friction was detected twice; as a consequence, JAXA has been monitoring the condition. On October 4, 2011, the AMSR-E reached its limit to maintain the rotation speed necessary for regular observations (40 rpm), and the radiometer automatically halted its observations and rotation. Although, JAXA continued to analyze this problem, and take necessary measures to correct the situation in cooperation with NASA, the AMSR-E mission came to an end. The cause of the failure is most likely due to aging lubricant in the bearing mechanism. 19)

The good news is that AMSR2, a slightly modified and improved version of AMSR-E, will be launched in 2012 on JAXA’s GCOM-W1 satellite, and will join Aqua and the other satellites in NASA’s A-Train constellation of Earth observation satellites. - The Aqua project had hoped that AMSR-E would provide at least one year of data overlap with the new AMSR2 instrument on GCOM-W1. 20)

• The Aqua spacecraft and its payload are operating nominally in 2011 with five of the six original Earth-observing instruments still operating well (these are: AIRS, AMSU, AMSR-E, MODIS, and CERES). It now looks like there is a good chance that the mission can continue at least to 2020. 21)


Figure 10: MODIS image of phytoplankton bloom in the Barents Sea observed on August 14, 2011 (image credit: NASA)

Legend to Figure 10: Brilliant shades of blue and green explode across the Barents Sea in this natural-color image taken on August 14, 2011, by MODIS on the Aqua spacecraft. Phytoplankton are tiny, microscopic plant-like organisms, but when they get together and start growing they can cover hundreds of square kilometers and be easily visible in satellite images. When conditions are right, phytoplankton populations can grow explosively, a phenomenon known as a bloom. A bloom may last several weeks, but the life span of any individual phytoplankton is rarely more than a few days. The area in this image is immediately north of the Scandinavian peninsula. Blooms spanning hundreds or even thousands of kilometers occur across the North Atlantic and Arctic Oceans every year. 22)

• The Aqua spacecraft and its payload are operating nominally in 2010. The Aqua sensors contain much synergy with each other and with other sensors and satellite platforms (e.g. Terra), and global climate model simulations. Many of these synergies have been explored, resulting in improved accuracy of core and new bio and geophysical products, and new understanding of the environment. - NASA hopes to continue the Aqua mission until at least the NPP mission is going to be launched in late 2011.

• The prime mission of Aqua was completed in September 2008. Five of the original six Aqua instruments are still operational and in good health, and should continue to operate successfully over the next four years (FY10-FY13) of the proposed continuation and beyond. In 2009, Aqua has adequate propellant for at least eight more years of normal operations. 23)

Scientific accomplishments and current merits of the Aqua platform are excellent. These merits include data and discoveries from approximately 100 data products that address each of NASA’s six interdisciplinary Earth science focus areas and 12 Applied Science Program Elements. The Aqua data are considered to be critical for the activities associated with the current or upcoming IPCC Working Group 1 Assessment Report 5 (AR5), 2009–2012, for regional to global climate change assessment and forecasting studies.

• Aqua is operating nominally in 2005. 24)

• The HSB (Humidity Sounder for Brazil) instrument of INPE ceased operating in February 2003.

• The AIRS instrument, the first high-spectral-resolution infrared sounder developed by NASA/JPL, has provided the most significant increase in forecast improvement in this time range of any other single instrument.

• Nominal Aqua mission operations began on September 1, 2002.



Sensor complement: (AIRS, AMSU/HSB, AMSR-E, CERES, MODIS)

Aqua has six Earth-observing instruments on board, collecting a variety of global data sets. 25)

Note: The descriptions of CERES and MODIS can be found under Terra.




Spectral resolution

Geophysical parameters



BAE Systems

More than 2,300 spectral channels ranging from 0.4 µm to 15.4 µm

Atmospheric temperature and humidity, land and sea surface temperatures, cloud, radioactive energy flux



JAXA (Japan)

12 channels at six discrete frequencies from 6.9 GHz to 89 GHz

Precipitation rate, water vapor, surface moisture content, sea ice extent, snow extent




15 channels ranging from 50 GHz to 90 GHz

Atmospheric temperature and humidity




Five channels ranging from 150 MHz to 183 MHz

Atmospheric humidity




Cross-track and azimuthal scanners with three channels per scanner

Radiative energy flux



Raytheon (SBRS)

36 channels ranging from 0.4 µm to 14 µm

Cloud, radioactive energy flux, aerosols, land cover and land use change, vegetation dynamics, land surface temperature, sea surface temperature, ocean color, snow cover, atmospheric temperature and humidity, sea ice

Table 1: Overview of sensor complement on the Aqua spacecraft


AIRS (Atmospheric Infrared Sounder):

AIRS is a NASA/JPL instrument, PI: M. T. Chahine; prime contractor is BAE Systems (Infrared and Imaging Systems Division (LMIRIS) of BAE Systems, in Lexington, MA). AIRS, along with AMSU and HSB, is of HIRS and MSU heritage flown on the NOAA POES series. Objective: High-spectral-resolution measurement of global temperature/humidity profiles in the atmosphere in support of operational weather forecasting by NOAA. Measurement of the Earth's upwelling infrared radiances in the spectral range of 3.74 - 15.4 µm, simultaneously at 2378 frequencies (bands). Four visible wavelength channels are also present. 26) 27) 28) 29) 30) 31) 32)


Figure 11: Photo of the AIRS instrument (image credit: NASA)

The AIRS spectrometer is a pupil imaging, multi-aperture echelle grating design that utilizes a coarse 13 lines/mm grating at high orders (3-11) to disperse infrared energy across a series of detector arrays. The typical entrance slit of a spectrometer is subdivided into a series of eleven apertures, each of which is imaged onto the focal plane. The grating serves to spectrally disperse each image, which in turn is overlaid onto a HgCdTe detector array with each detector in the array viewing a unique wavelength by virtue of the grating dispersion. Rejection of overlapping grating orders and background photon suppression is provided by a series of IR bandpass filters located within the spectrometer and directly on the focal plane. Use of the grating in combination with the filter set provides a two-dimensional color map on the focal plane with a high degree of design flexibility in terms of color arrangement and spacing. Cooling of the spectrometer to 155 K is provided by a two stage passive radiator assembly with 10 Watt cooling capacity at 155 K.


Figure 12: Isometric view of the AIRS instrument (image credit: NASA/JPL)

Dispersed energy exiting the spectrometer is imaged onto a state-of-the-art hybrid PV/PC: HgCdTe focal plane assembly (FPA) consisting of a series of multi-linear arrays each associated with a specific entrance aperture. The assembly consists of 17 arrays arranged in 12 modules with each module individually optimized for wavelength and photon flux. The module set includes 10 photovoltaic (PV) modules covering the 3.7 - 13.7 µm region and 2 photoconductive (PC) modules for the 13.7 - 15.4 µm region. The more advanced PV modules include on-focal plane signal processing via a custom CMOS Readout IC (ROIC) specifically designed for AIRS temperature, photon flux and radiation conditions. The ROIC provides the first stage of signal integration at a 1.4 ms subsample rate, which are summed off focal plane in groups of 16 to meet full footprint dwell time requirements. The IR FPA provides simultaneous measurement of 2378 spectral samples across the 3.7 - 15.4 µm region with two samples per resolution element. Additionally, each PV sample is further divided by two in the cross-dispersed direction to provide increased yield and a measure of spectral redundancy. As a consequence, the IR FPA contains a total of 4482 active detectors. The complex FPA is packaged in a vacuum dewar maintained at the 155 K spectrometer operating temperature, with the IR FPA cooled to 58 K via a redundant, 1.5 W capacity Split Stirling pulse tube cryocooler.


Figure 13: Illustration of the FPA (Focal Plane Assembly), image credit: NASA/JPL)


Figure 14: The AIRS spectrometer assembly (image credit: NASA/JPL)


Figure 15: AIRS scan assembly (image credit: NASA/JPL)


Figure 16: Illustration of the cryocooler assembly (image credit: NASA/JPL)

The infrared region of 3.74-15.4 µm has a spectral resolution of 1200 (lambda/ delta lambda). The high spectral resolution permits the separation of unwanted spectral emissions and, in particular, provides spectrally clean “super windows,” ideal for surface observations. - This is supplemented by a VNIR photometer of four bands in the range between 0.4 and 1.0 µm. The VNIR channels are used to discriminate between low-level clouds and different terrain and surface covers, including snow and ice. The AIRS infrared bands have an IFOV of 1.1º and FOV = ± 49.5º scanning capability perpendicular to the spacecraft ground track (swath width = 1650 km, 13.5 km horizontal resolution in nadir, 1 km vertical). It takes 22.41 ms for each footprint of 1.1º in diameter (or 13.5 km). Each IR scan produces 90 footprints across the flight track and takes 2.67 s (see Figure 17). The VNIR channels have a footprint of 0.185º or about 2.3 km on the ground, nine VNIR footprints are within a 40 km swath. The VNIR photometer is boresighted to the spectrometer to allow simultaneous VNIR observations.

The VNIR photometer uses optical filters to define the four spectral bands. It operates at ambient temperatures (293-300 K). Inflight calibration is performed during each scan period. In addition, AIRS uses four independent cold-space views.

The major data products derived from AIRS are atmospheric temperature profiles, humidity profiles (from channels in the 6.3 µm water vapor band and the 11 µm windows, sensitive to the water vapor continuum), and land skin surface temperature.

AIRS is flown on the Aqua satellite with two operational microwave sounders: NOAA's AMSU and Brazil's HSB (Humidity Sounder Brazil). Together, the three sensors constitute constitute a possible advanced operational sounding system for future NOAA missions - offering increased accuracy of short-term weather predictions, improved tracking of severe weather events like hurricanes, and advances in climate research.

Instrument type

Multi-aperture, non-Littrow echelle array grating spectrometer configuration

Spectral coverage

3.74 - 15.4 µm for the array grating spectrometer (IR bands)
0.4 - 1.0 µm for photometer (4 VNIR bands at: 0.41-0.44, 0.58-0.68, 0.71-0.92, 0.49-0.94 µm)

Spectral resolution

1200 (lambda/delta lambda) array grating spectrometer, 2378 bands

Spatial resolution

13.5 km horizontal at nadir for IR bands (IFOV = 1.1º), 1 km vertical resolution, 2.3 km x 2.3 km for VNIR bands (IFOV = 0.185º)

IR detector cooling

Two-stage passive radiative cooler with retractable earth shield,

Swath width

1650 km (FOV= ± 49.5º) for IR bands; 40 km for VNIR bands

Instrument mass, power

177 kg, 220 W

Date rate, duty cycle

1.27 Mbit/s, 100%

Table 2: Overview of some AIRS parameters


Figure 17: Illustration of the AIRS scan geometry and coverage (image credit: NASA/JPL)


Some AIRS results in 2010:

The excellent sensitivity and stability of the AIRS instrument has recently allowed the AIRS team to successfully retrieve Carbon Dioxide (CO2) concentrations in the mid-troposphere (8-10 km) with a horizontal resolution of 100 km and an accuracy of better than 2 ppm. 33)

Originally designed to retrieve temperature and water vapor profiles for weather forecast improvement, the AIRS (Atmospheric Infrared Sounder) has become a valuable tool for the measurement and mapping of mid-tropospheric carbon dioxide concentrations. Several researchers have demonstrated the ability to retrieve mid-tropospheric CO2 from AIRS by different methods. The retrieval method selected for processing and distribution is called the method of “Vanishing Partial Derivatives” and results in over 15,000 CO2 retrievals per 24-hour period with global coverage and an accuracy better than 2 ppm.

The AIRS CO2 accuracy has been validated against a variety of mid-tropospheric aircraft measurements as well as upward looking interferometers (FTIR) from the ground.

Mid-tropospheric CO2 concentrations are an indicator for atmospheric transport and several interesting findings have resulted from analysis of the data.

- First is the non-uniformity of CO2, primarily caused by weather.

- Second is the ability to identify stratospheric-tropospheric exchange during a sudden stratospheric warming event.

- Third is the presence of a seasonally varying belt of enhanced CO2 concentrations in the Southern Hemisphere.


Figure 18: AIRS yields about 15,000 mid-tropospheric CO2 measurements per day (image credit: NASA/JPL)

Carbon dioxide turns out to be an excellent tracer gas since it does not react with other gases in the atmosphere. The project is finding that the AIRS mid-tropospheric CO2 is a good indicator of vertical motion in the atmosphere. It is a known fact that the majority of atmospheric CO2 is produced and absorbed near the surface and that there are no sources or sinks in the free troposphere. Thus elevated levels of mid-tropospheric CO2 are the result of airflow into the mid-troposphere from the near surface.

The most obvious finding from the AIRS retrievals is that the distribution of CO2 is not uniform as indicated in the models. Strong latitudinal and longitudinal gradients exist particularly over the large land masses in the Northern Hemisphere. This phenomenon is referred to as “CO2 weather”. The large variability in atmospheric circulation due to convection and global and mesoscale transport is responsible for most of the variability seen in the AIRS data. This implies that the AIRS CO2 data will be extremely useful for validating global scale transport in GCMs (Global Circulation Models).


Figure 19: AIRS mid-tropospheric CO2 is a tracer for atmospheric motion particularly in the vertical direction. July, 2010 monthly average (image credit: NASA/JPL)



AMSU/HSB (Advanced Microwave Sounding Unit (NASA Instrument)/ (Humidity Sounder for Brazil), provided by INPE. Both instruments operate in conjunction.

AMSU was designed and developed by Aerojet of Azusa, CA (a GenCorp company). AMSU primarily provides temperature soundings, whereas HSB provides humidity soundings. AMSU is a 15-channel microwave radiometer. AMSU and HSB have a total of 19 channels, 15 are assigned to AMSU, each having a 3.3º beamwidth, and four are assigned to HSB, each having a beamwidth of 1.1º. AMSU comprises two separate units: AMSU-A1 (channels 3-15), and AMSU-A2 (channels 1 and 2). Channels 3 - 14 use the 50 to 60 GHz oxygen band to provide data for vertical temperature profiles up to 50 km. The “window” channels (1, 2, and 15) provide data to enhance the temperature sounding by correcting for surface emissivity, atmospheric liquid water, and total precipitable water. HSB channels 17 - 20 use the 183.3 GHz water vapor absorption line to provide data for the humidity profile. 34) 35)

AMSU-A1 measures temperature profiles from the surface up to 50 km in 15 channels. Temperature resolution: 0.25 - 1.2 K. The AMSU-A1 instrument has two 15 cm diameter antennas (reflectors with momentum compensation), each with a 3.3º nominal IFOV at the half power points or FWHM (Full width Half maximum). Each antenna provides a cross-track scan of ±49.5º from nadir with a total of 30 Earth views (scan positions) per scan line. The total scan period is eight seconds. The footprint (resolution) at nadir is 40 km. The swath width is approximately 1690 km. Internal calibration is performed with internal warm loads and cold space.

AMSU-A2 has a single 28 cm diameter antenna (reflector without momentum compensation) with a 3.3º nominal IFOV. All other instrument/observation parameters are the same as those of AMSU-A1.

AMSU parameters: mass = 91 kg (49 kg for AMSU-A1, 42 kg for AMSU-A2); power = 101 W; data rate = 2.0 kbit/s; thermal control by heater, central thermal bus, radiator; thermal operating range= 0-20º C.



Center Frequency (GHz)

Bandwidth (MHz)

Sensitivity NEΔT (K)

(2 channels)





(13 channels)


53.596± 0.115
57.290344 = Flo
Flo ± 0.217
Flo ± 0.3222, (±0.048)
Flo ± 0.3222, (±0.022)
Flo ±0.3222, (± 0.010)
Flo ±0.3222, (± 0.0045)



(4 channels)





Table 3: Spectral parameters of the AMSU-A and HSB instruments


Figure 20: View of AMSU-A1 (left) and AMSU-A2 (right), image credit: Aerojet




Instrument size

72 cm x 34 cm x 59 cm

73 cm x 61 cm x 68 cm

Mass, power

49 kg, 72 W

42 kg

Data rate

1.3 kbit/s

0.4 kbit/s

Antenna size

15 cm (2 units)

31 cm (1 unit)

IFOV (Instantaneous Field of View)



Swath width

100º, 1650 km

100º, 1650 km

Pointing accuracy



No of channels



Table 4: Summary of AMSU instrument parameters


HSB (Humidity Sounder for Brazil):

HSB is an INPE-provided instrument of AMSU-B heritage (built by MMS (Matra Marconi Space) of Bristol, UK (now EADS Astrium Ltd) with participation of Equatorial Sistemas of Brazil), and sponsored by AEB (Brazilian Space Agency). HSB is a microwave radiometer with the objective to measure atmospheric radiation, to obtain atmospheric water vapor profile measurements and to detect precipitation under clouds with 13.5 km horizontal nadir resolution (humidity profiles for weather foresting). 36) 37) 38)

HSB is a four-channel self-calibrating instrument (passive sounder) providing a humidity profiling capability in the frequency range of 150 - 190 GHz, spanning the height from surface to about 42 km. The measured signals are also sensitive to a) liquid water in clouds (cloud liquid water content) and b) graupel and large water droplets in precipitating clouds (qualitative estimate of precipitation rate). HSB scans in the cross-track direction at a rate of 2.67 seconds in continuous mode. The instrument features a momentum-compensated scan mirror system. HSB is operated in combination with AMSU-A, they have a total of 19 channels: 15 are assigned to AMSU-A, each having a 3.3º beamwidth, and four assigned to HSB, each having a 1.1º beamwidth. The HSB receiver channels are configured to operate in DSB (Double Sideband).

The HSB collected valuable data for the first nine months of the mission but ceased operating in February 2003 (scanner anomaly).

Nr. of channels

4 (total), Ch 17 at 150 GHz, Ch 18: 183.31 ±1 GHz, Ch. 19: 183.31 ±3 GHz, and Ch 20: 183.31 ±7 GHz

Swath width, scan period

1650 km, 2.67 s


±49.5º cross track from nadir (+90º to -49.5º for calibration)

IFOV (spatial resolution)

1.1º (13.5 km at nadir)

Instrument pointing

Control = 3600 arcseconds, knowledge = 360 arcseconds,
stability = 74 arcseconds/s

Thermal control, operating range

Radiator, 13 - 35ºC

Instrument power

80 W average, 154 W peak

Instrument mass, size, data rate

51 kg, 70 cm x 65 cm x 46 cm, 4.2 kbit/s

Temperature accuracy (data profile)

1.0 - 1.2 K, coverage (twice daily) of land and ocean surfaces, resolution of 50 km (horiz.) and 1 km (vertical), up to 100 mb

Humidity accuracy (data profile)

20%, global coverage (twice daily), res. = 50 km, 1 km (vertical)

Radiance accuracy (data profile)

1-1.2 K, global coverage (twice daily), res. = 15 km (average)

Table 5: Specification of the HSB instrument


Figure 21: Photo of the HSB instrument (image credit: NASA)


AMSR-E (Advanced Microwave Scanning Radiometer-EOS):

AMSR-E is a JAXA/NASA cooperative instrument, of AMSR heritage, built by Mitsubishi Electronics Corporation (PIs: A. Shibata, R. W. Spencer). The objective is the measurement of geophysical parameters such as: cloud properties, radiative energy flux, precipitation, land surface wetness (moisture), sea ice, snow cover, sea surface temperature (SST), and sea surface wind fields. AMSR-E is a modified design of AMSR on ADEOS-II (Japan).

The AMSR-E instrument is a conically scanning total power passive microwave radiometer sensing microwave radiation (brightness temperatures) at 12 channels and 6 frequencies ranging from 6.9 to 89.0 GHz (6.925, 10.65, 18.7, 23.8, 36.5, and 89.0 GHz). Horizontally and vertically polarized radiation are measured separately at each frequency. 39) 40) 41)

AMSR-E consists of an offset parabolic reflector 1.6 m in diameter, fed by an array of six feedhorns. The reflector and feedhorn arrays are mounted on a drum which contains the radiometers, digital data subsystem, mechanical scanning subsystem, and power subsystem. The reflector/feed/drum assembly is rotated about the axis of the drum by a coaxially mounted bearing and power transfer assembly. All data, commands, timing and telemetry signals, and power pass through the assembly on slip ring connectors to the rotating assembly. The AMSR-E instrument has a mass of 314 kg, power = 350 W, a duty cycle of 100%, and an average data rate of 87.4 kbit/s.

Center frequency (GHz)







Bandwidth (MHz)







Sensitivity (K)







IFOV (km x km) footprint

75 x 43

51 x 29

27 x 16

31 x 18

14 x 8

6 x 4

Sampling rate (km x km)

10 x 10

10 x 10

10 x 10

10 x 10

10 x 10

5 x 5

Integration time (ms)







Main beam efficiency (%)







Beamwidth (º)








Horizontal and Vertical

Incidence angle



Cross polarization

< - 20 dB

Swath width

> 1450 km

Dynamic range

2.7 - 340 K

Data quantization

12 bit

10 bit

Data rate

87.4 kbit/s

Antenna size, control unit

1.95 m x 1.7 m x 2.4 m, 0.8 m x 1.0 m x 0.6 m

Table 6: Performance parameters of AMSR-E


Figure 22: Schematic view of the AMSR-E instrument (image credit: NASA)

The AMSR-E instrument rotates continuously about an axis parallel to the local spacecraft vertical at 40 rpm. At an altitude of 705 km, it measures the upwelling scene brightness temperatures over an angular sector of ± 61º about the subsatellite track, resulting in a swath width of 1445 km. During a period of 1.5 seconds the S/C subsatellite point travels 10 km. Even though the IFOV for each channel is different, active scene measurements are recorded at equal intervals of 10 km (5 km for the 89 GHz channels) along the scan. The half cone angle at which the reflector is fixed is 47.4º which results in an Earth incidence angle of 55.0º.


Figure 23: Line drawing of the AMSR-E instrument (image credit: NASA)

Instrument calibration. The radiometer calibration accuracy budget, exclusive of antenna pattern correction effects, is composed of three major contributors: warm load reference error, cold load reference error, radiometer electronics nonlinearities and errors.

Some data products from AMSR-E are:

• Level 2A brightness temperatures

• Level 2 rainfall

• Level 3 rainfall

• Columnar cloud water over the oceans

• Columnar water vapor over the oceans

• Sea surface temperature (SST)

• Sea surface wind speed

• Sea ice concentration

• Sea ice temperature

• Snow depth on sea ice

• Snow-water equivalent on land

• Surface soil moisture


Figure 24: The Aqua spacecraft and instrument accommodations (image credit: NASA, JAXA)

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27) Aqua brochure of NASA/GSFC, March 2002, courtesy of Claire L. Parkinson, URL:


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32) Stuart MacCallum, “The Atmospheric InfraRed Sounder,” 2005, URL:

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35) Eric J. Fetzer, Edward T. Olsen, Luke Chen, Denise Hagan, “Validation of AIRS / AMSU / HSB retrieved products,” URL:

36) Information provided by Janio Kono of INPE, Sao José dos Campos, Brazil

37) B. H. Lambrigtsen, R. V. Calheiros, “The Humidity Sounder for Brazil - an international partnership,” IEEE Transaction on Geoscience and Remote Sensing, Vol. 41, Issue 2, Feb. 2003, pp. 352-361

38) Ezio Castejon Garcia, Marcio Bueno dos Santos, “The Environmental Simulation of the Humidity Sounder for Brazil,” 54th Astronautical Congress of the IAF, Sept. 29 - Oct. 3, 2003, Bremen, Germany


40) AMSR-E Data Users Handbook, 4th Edition, JAXA, March 2006, NCX-030021


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.