Fumihiro Sakuma

The functional evaluation model for the on-board hyperspectral radiometer

The hyper-multi spectral mission named HISUI (Hyper-spectral Imager SUIte) is the next Japanese earth observation project that will be on board ALOS-3 satellite. This project is the follow up mission of the Advanced Spaceborne Thermal Emission and reflection Radiometer (ASTER). HISUI is composed of hyperspectral radiometer with higher spectral resolution and multi-spectral radiometer with higher spatial resolution. The functional evaluation model is under development to confirm the spectral and radiometric performance prior to the flight model manufacture phase. This model contains the VNIR and SWIR spectrograph, the VNIR and SWIR detector assemblies with a mechanical cooler for SWIR, signal processing circuit and on-board calibration source.

Onboard calibration of the ASTER instrument over twelve years

The ASTER is a high-resolution optical sensor for observing the Earth on the Terra satellite launched in December1999. The ASTER consists of three radiometers. The VNIR has three bands in the visible and near-infrared region, the SWIR has six bands in the shortwave infrared region, and the TIR has five bands in the thermal infrared region. The onboard calibration devices of the VNIR and SWIR were halogen lamps and photodiode monitors. In orbit three bands of the VNIR showed a rapid decrease in the output signal. The band 1, the shortest wavelength, decreased most to 70% in twelve years. The temperature of the onboard blackbody of the TIR is varied from 270 K to 340 K in the long term calibration for the offset and gain calibration. The long term calibration of the TIR showed a decrease in response after launch. The decrease was most remarkable at band 12 decreasing to 60% in eleven years. The degradation spectra of the TIR shows that the possible causes of the degradation might be silicone and hydrazine. ASTER onboard calibration is normally carried out once in 49 days but additional onboard calibrations were added just before and after the inclination adjustment maneuver (IAM) to check the effect on the RCC. This experiment was carried out three times for each IAM in the fiscal year 2011. The result showed that the change in the RCC was small for both VNIR and TIR.

A compact thermal infrared imaging radiometer with high spatial resolution and wide swath for a small satellite using a large format uncooled infrared focal plane array

In this paper, we present a feasibility study for the potential of a high spatial resolution and wide swath thermal infrared (TIR) imaging radiometer for a small satellite using a large format uncooled infrared focal plane array (IR-FPA). The preliminary TIR imaging radiometer designs were performed. One is a panchromatic (mono-band) imaging radiometer (8-12μm) with a large format 2000 x 1000 pixels uncooled IR-FPA with a pixel pitch of 15 μm. The other is a multiband imaging radiometer (8.8μm, 10.8μm, 11.4μm). This radiometer is employed separate optics and detectors for each wave band. It is based on the use of a 640 x 480 pixels uncooled IR-FPA with a pixel pitch of 25 μm. The thermal time constant of an uncooled IR-FPA is approximately 10-16ms, and introduces a constraint to the satellite operation to achieve better signal-to-noise ratio, MTF and linearity performances. The study addressed both on-ground time-delayintegration binning and staring imaging solutions, although a staring imaging was preferred after trade-off. The staring imaging requires that the line of sight of the TIR imaging radiometer gazes at a target area during the acquisition time of the image, which can be obtained by rotating the satellite or a steering mirror around the pitch axis. The single band radiometer has been designed to yield a 30m ground sample distance over a 30km swath width from a satellite altitude of 500km. The radiometric performance, enhanced with staring imaging, is expected to yield a NETD less than 0.5K for a 300K ground scene. The multi-band radiometer has three spectral bands with spatial resolution of 50m and swath width of 24km. The radiometric performance is expected to yield a NETD less than 0.85K. We also showed some preliminary simulation results on volcano, desert/urban scenes, and wildfire.

Onboard electrical calibration of the ASTER VNIR

The Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) is one of the five sensors on the NASA’s Terra satellite on orbit since December 1999. ASTER consists of three radiometers, the Visible and Near InfraRed (VNIR), the Short-Wave InfraRed (SWIR) and Thermal InfraRed (TIR) whose spatial resolutions are 15 m, 30 m and 90 m, respectively. Unfortunately the SWIR image data are saturated since April 2008 due to the offset rise caused by the cooler temperature rise, but the VNIR and the TIR are taking Earth images of good quality. The VNIR and the TIR experienced responsivity degradation while the SWIR showed little change. From the lamp calibration, Band 1 decreased the most among three VNIR bands and 31% in thirteen years. The VNIR has the electrical calibration mode to check the healthiness of the electrical circuits through the charge coupled device (CCD). Four voltage levels from Line 1 to Line 4, which are from 2.78 V to 3.10 V, are input to the CCD in the onboard calibration sequence and the output digital numbers (DNs) are detected in the images. These input voltages are monitored as telemetry data and have been stable up to now. From the electrical calibration we can check stabilities of the offset, gain ratio and gain stability of the electric circuit. The output level of the Line1 input is close to the offset level which is measured while observing the earth at night. The trend of the Line 1 output is compared to the offset level. They are similar but are not exactly the same. The trend of the even pixel and odd pixel is the same so the saturated offset levels of the odd pixel is corrected by using the even pixel trend. The gain ratio trend shows that the ratio is stable. But the ratio values are different from those measured before launch. The difference comes up to 10% for the Band 2. The correct gain ratio should be applied to the vicarious calibration result because the onboard calibration is measured with the Normal gain whereas the vicarious calibration often measures with the High gain. The cause of the VNIR responsivity degradation is not known but one of the causes might be the change of the electric circuit. The band 3 gain shows 16 % decrease whereas the gain changes of the band 1 and band 2 are 5% to 8%. The responsivity decrease after 1000 days since launch might be controlled by the electric circuit change.

Eleven years of ASTER onboard calibration

The ASTER is a high-resolution optical sensor for observing the Earth on the Terra satellite launched in December1999. The ASTER consists of three radiometers. The VNIR has three bands in the visible and near-infrared region, the SWIR has six bands in the shortwave infrared region, and the TIR has five bands in the thermal infrared region. The onboard calibration devices of the VNIR and SWIR were halogen lamps and photodiode monitors. In orbit three bands of the VNIR showed a rapid decrease in the output signal. The band 1, the shortest wavelength, decreased most to 70% in eleven years. The VNIR spectra of the responsivity degradation were compared to other sensors, the JERS-1 OPS, the OCTS, the Hyperion, the MODIS, the MISR and the SPOT. The temperature of the onboard blackbody of the TIR is varied from 270 K to 340 K in the long term calibration for the offset and gain calibration. The long term calibration of the TIR showed a decrease in response after launch. The decrease was most remarkable at band 12 decreasing to 60% in eleven years. The degradation spectra of the TIR shows that the possible causes of the degradation might be silicone and hydrazine.

Retrieval of spectral response functions for the hyperspectral sensor of HISUI (Hyperspectral Imager SUIte) by means of onboard calibration sources

HISUI (Hyper-spectral Imager SUIte), which is the next Japanese earth observation project, has been developed under the contract with Ministry of Economy, Trade and Industry(METI) and New Energy and Industrial Technology Development Organization(NEDO). HISUI is composed of hyper-spectral sensor and multi-spectral sensor. The hyperspectral sensor is an imaging spectrometer with two separate spectral channels: one for the VNIR range from 400 to 970 nm and the other for the SWIR range from 900 to 2500 nm. Ground sampling distance is 30 m with spatial swath width of 30 km. The spectral sampling will be better than 10 nm in the VNIR and 12.5 nm in the SWIR. The multi-spectral sensor has four VNIR spectral bands with spatial resolution of 5m and swath width of 90 km. HISUI will be installed in ALOS-3 that is an earth observing satellite in the project formation phase by JAXA in FY 2015. This paper is concerned with the retrieval of spectral response functions (SRF) for the hyper-spectral sensor. The center wavelength and bandwidth of spectral response functions of hyper-spectral sensor may shift and broaden due to the distortion in the spectrometer, the optics and the detector assembly. Therefore it is necessary to measure or estimate the deviation of the wavelength and the bandwidth broadening of the SRFs. In this paper, we describe the methods of retrieval of the SRFs parameters (Gaussian functions assumed) by means of onboard calibration sources and we show some simulations results and the usefulness of this method.

ASTER VNIR 15 years growth to the standard imaging radiometer in remote sensing

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Visible and Near Infrared Radiometer (VNIR) is the remote sensing equipment which has 3 spectral bands and one along-track stereoscopic band radiometer. ASTER VNIR’s planned long life design (more than 5 years) is successfully achieved. ASTER VNIR has been imaging the World-wide Earth surface multiband images and the Global Digital Elevation Model (GDEM). VNIR data create detailed world-wide maps and change-detection of the earth surface as utilization transitions and topographical changes. ASTER VNIR’s geometric resolution is 15 meters; it is the highest spatial resolution instrument on NASA’s Terra spacecraft. Then, ASTER VNIR was planned for the geometrical basis map makers in Terra instruments. After 15-years VNIR growth to the standard map-maker for space remote-sensing. This paper presents VNIR’s feature items during 15-year operation as change-detection images , DEM and calibration result. VNIR observed the World-wide Earth images for biological, climatological, geological, and hydrological study, those successful work shows a way on space remote sensing instruments. Still more, VNIR 15 years observation data trend and onboard calibration trend data show several guide or support to follow-on instruments.

ASTER system operating achievement for 15 years on orbit

ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) System is operating more than 15 years since launched on board of NASA’s Terra spacecraft in December 1999. ASTER System is composed of 3 radiometers (VNIR (Visible and Near Infrared Radiometer), SWIR (Short-Wave Infrared Radiometer), and TIR (Thermal Infrared Radiometer)), CSP (Common Signal Processor) and MSP (Master Power Supply). This paper describes the ASTER System operating history and the achievement of ASTER System long term operation since the initial checkout operation, the normal operation, and the continuous operation. Through the 15 years operation, ASTER system had totally checked the all subsystems (MPS, VNIR, TIR, SWIR, and CSP) health and safety check using telemetry data trend evaluation, and executed the necessary action. The watch items are monitored as the life control items. The pointing mechanics for VNIR, SWIR and TIR, and the cooler for SWIR and TIR are all operating with any problem for over 15 years. In 2003, ASTER was successfully operated for the lunar calibration. As the future plan, ASTER team is proposing the 2nd lunar calibration before the end of mission.

ASTER TIR onboard calibration over fourteen years

The ASTER Instrument is one of the five sensors on the NASA’s Terra satellite on orbit since December 1999. After 14 years on orbit, ASTER VNIR and TIR are still taking Earth images of good quality. The TIR radiometer has five bands from 8 to 12 μm with spatial resolution of 90 m. Each band has ten detectors. The detectors are cooled at 80 K precisely by using a Stirling cooler within 0.1 K. TIR is radiometrically calibrated by a single onboard blackbody. In the normal operation mode the blackbody is kept at 270 K, and once in 49 days the blackbody is heated up to 340 K for the gain calibration. The degradation at band 12 is largest and 48% and that at band 10 is smallest and 18%. One of the possible causes of the degradation is the contamination accretion by outgas of silicone SE9188 RTV used for TIR followed by the ultraviolet radiation. The absorption spectra of outgas of this silicon was measured at JAXA and the absorption spectra showed similar to the TIR degradation in the early days on orbit. ASTER science team is proposing the second lunar calibration at the end of terra mission for the estimation of the TIR optical characteristics. ASTER experienced first lunar calibration in April 2003 and many of the TIR bands were saturated. Due to the responsivity degradation the TIR dynamic range has extended to higher temperature. At least TIR four bands will not saturate in the next lunar calibration.

Effect of temperature on onboard calibration reference material for spectral response function retrieval of the hyperspectral sensor of HISUI-SWIR spectral case

HISUI (Hyperspectral Imager SUIte) is the next Japanese earth observation sensor, which consists of hyperspectral and multispectral sensors. The hyperspectral sensor is an imaging spectrometer with the VNIR (400-970nm) and the SWIR (900-2500nm) spectral channels. Spatial resolution is 30 m with swath width of 30km. The spectral resolution will be better than 10nm in the VNIR and 12.5nm in the SWIR. The multispectral sensor has four VNIR spectral bands with spatial resolution of 5m and swath width of 90km. HISUI will be installed in ALOS-3 that is an earth observing satellite by JAXA. It will be launched in FY 2015. This paper is concerned with the effect of temperature on onboard calibration reference material (NIST SRM2065) for spectral response functions (SRFs) retrieval of the hyperspectral sensor. Since the location and intensity of absorption features are sensitive to material temperature, the estimated center wavelength and bandwidth of the SRFs may include the uncertainty. Therefore, it is necessary to estimate the deviation of the wavelength and the bandwidth broadening of the SRFs when the material temperature changes. In this paper we describe the evaluation of uncertainty of the SRF’s parameters retrieval and show some simulation’s results.