The PRISMA hyperspectral mission: science activities and opportunities for agriculture and land monitoring Pignatti Stefano, Palombo Angelo, Pascucci Simone, Romano Filomena, Santini Federico, Simoniello Tiziana, Amato Umberto, Cuomo Vincenzo.
Casa Raffaele Università degli Studi della Tuscia, DAFNE Viterbo, Italy
CNR IMAA - IAC C.da S. Loja, 85050 Tito, Italy
[email protected]
De Bonis Roberto, Laneve Giovanni Università di Roma “La Sapienza”, DIAEE Rome, Italy
Nicola Acito, Diani Marco, Matteoli Stefania, Corsini Giovanni
Ananasso Cristina ASI, Agenzia Spaziale Italiana Rome, Italy
Università di Pisa, IET Pisa, Italy
Abstract—The main objectives of the PRISMA (Hyperspectral Precursor of the Application Mission) mission are: the implementation of an Earth Observation pre-operative payload, the in-orbit demonstration and qualification of an Italian state-of-the-art hyperspectral/panchromatic technology and the validation of end-to-end data processing system able to support the development of new applications based on high spectral resolution images. The aim of the paper is to provide an overview of the PRISMA mission by describing the current status of the program and giving a brief outline of the work done till now in the framework of the SAP4PRISMA project scientific studies in supporting the exploitation of the future PRISMA hyperspectral images for environmental applications. Keywords—PRISMA mission; hyperspectral satellite data; agricultural applications; land monitoring applications
I. PRISMA PAYLOAD The PRISMA payload, completely funded by ASI, is conceived as a “public good” pre-operational and technology demonstrator mission, focused on the qualification of a space based panchromatic (PAN) and hyperspectral (HSI) payload and for the delivery of panchromatic/hyperspectral products. PRISMA payload is characterized by a single telescope shared between the panchromatic and the hyperspectral sensors. The expected set of data allow for detailed environmental monitoring, characterization and extraction of parameters suitable for rock/soil targets analysis, vegetation, ecosystem and inland and coastal waters monitoring. PRISMA HSI has the capability to collect 240 spectral bands in the wavelength range 400 - 2450 nm. A silicon based detector system was selected for the VNIR range from 420 nm
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to 1010 nm, while the SWIR camera features a MCT diode array being sensitive from 920 nm to 2505 nm. The total number of downloadable bands is still subject to a revision process that takes into account the bands’ SNR and the images swath, to stay within the throughput of the Payload Data Handling and Transmission (PDHT). Since HSI uses as disperser a prism, it is characterized by a non linear spectral dispersion with an average Spectral Sampling Interval (SSI) of 9.4 nm and 9.3 nm for the 63 VNIR bands and for the 171 SWIR bands, respectively (Table 1). For the SWIR spectrometer the spacing of the average spectral channels is 10nm on average which is sufficient to resolve the typical mineralogical features around 2000 nm while guaranteeing an acceptable SNR in the range where solar irradiation is poor. The most recent payload simulation gives as output bands with SNR acceptable and suitable enough to fit the mission requirements as well as the operational requirements defined by the scientific community supporting ASI. The radiometric calibration system on board is designed to perform recurrently the (a) absolute radiometric calibration using the sun as the source; (b) relative radiometric calibration, spectral calibration and linearity assessment with two tungsten lamps optimized for the VNIR and SWIR; (c) calibration of the dark with the shutter slit. However, on demand calibrations involving platform maneuvers can be performed and they include: flat-field external, observation of specific test areas on earth, observing the moon. Each calibration procedure is designed so that the entire pupil and the entire FOV of the instrument are illuminated and the optical path of the radiation reference is the same as the radiation observed.
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TABLE I. Parameter Spectral range Spectral resolution (FWHM) Spectral bands
VNIR channel 400-1010 nm
SWIR channel 920-2500 nm
Pan channel 400-750 nm
12 nm
12 nm
-
66
1
SNR (Signalto-Noise Ratio)
> 200 in the range 0.4-1.0 μm >600 @ 0.65 μm
171 > 200 @1.0-1.75 μm > 400 @ 1.55 μm > 100 @ 1.95-2.35 μm > 200 @ 2.1 μm
MTF Swath width Spatial resolution Spatial detector pixels IFOV Telescope type Telescope aperture
• Level 2d: HYP and PAN geocoded at-surface Reflectance Product
PRISMA PAYLOAD, MAIN CHARACTERISTICS
> 0.3 @ Nyquist frequency
> 0.3 @ Nyquist frequency
Moreover, a scientific support for value-added products (L3/L4) has been funded by ASI and is still ongoing. III.
The applications domain of the national interest identified for the PRISMA mission can be summarized in the following: (a) detailed mapping of land cover, land cover changes and functions; (b) agricultural crop mapping and characterization, (c) desertification, and hazard monitoring (e.g., fires, landslides, etc.); (d) coastal zones, Mediterranean sea and inland waters quality assessment and monitoring; (e) carbon cycle monitoring; (f) urban functional areas mapping and monitoring; (g) land surface hydrology and water management.
240
> 0.2 @ Nyquist frequency
30 km (FOV = 2.77º) 30 m
5m
1000 x 256 with 30 μm pitch
6000
48.34 μrad TMA (Three Mirror Anastigmat) 210 mm diameter
The HSI works in a push-broom mode designed to operate in a sun synchronous orbit at a height of 620 Km crossing the Equator at the orbit descending node at 10:30 local time. The optical design (IFOV 48.4 μrad, FOV 2.77°) will assure the HSI images at the GSD of 30m for each operative mode. The program is at present in phase C and it is scheduled to be launched for 2015. II.
THE SAP4PRISMA PROJECT
PRISMA PRODUCTS
The PRISMA mission products levels are foreseen to cover levels from 0 (raw data) to 2D (corresponding to reflectance and radiance geocoded over terrain): • Level 0 products: HYP and PAN reformatted instrument data packets with appended metadata, including ancillary data and file formatting information) • Level 1 product: HYP and PAN calibrated Top of Atmosphere Radiance - TOA including Cloud Mask, Sunglint Mask, General Classification Mask and Characterization and Calibration Data
More specifically, concerning the SAP4PRISMA project (“Development of algorithms and products for agriculture and land monitoring applications for supporting the PRISMA mission”), the main objective is to develop hyperspectral data processing optimal algorithms and mature products that meet the real needs of end users also keeping in mind the real potential of the sensor in terms of spectral coverage, spatial and temporal frequency of acquisitions [1]. Therefore, the SAP4PRISMA project is focusing its research activities on those geophysical parameters or applications that are suitable for the characteristics of the mission and in perspective for any satellite of the future hyperspectral constellation (see option offered by other next HSI such as EnMap, HYSPIRI and HISUI and the advent of the Sentinel-2 images with their high temporal frequency and data policy). SAP4PRISMA is structured in interconnected research activities aimed at consolidating, with respect to the PRISMA sensor characteristics, the methodological issues for retrieving geophysical and agro-environmental parameters for improved modeling and understanding of biosphere and geosphere processes. By this way it is possible to better understand Earth’s surface processes and start the development of innovative complex high value products (e.g., nitrate leaching, land degradation and fuel maps). To achieve these specific objectives, the project focuses also on data quality and preprocessing research themes.
• Level 2b: Geolocated at Ground Radiance Product (obtained by applying atmospheric correction)
The project aims at defining a robust processing chain for retrieving agro-environmental parameters related mainly to agricultural and land degradation topics. Processing chain that accounts also the aspects related to the quality evaluation, data enhancing, data correction, image enhancement and classification (i.e. hard and soft). The project main applicative issues are: (a) land degradation and vegetation status, (b) products development for agricultural areas, (c) management and monitoring of natural and induced hazards.
• Level 2c: Geolocated At-surface Reflectance Product (obtained by applying atmospheric correction, processed optionally using Ground Control Points - GCP), Aerosol Characterization Product (VNIR, to provide aerosol optical thickness and Angstrom exponent maps, with appended geolocation coefficients), Water Vapor Map Product (only HYP), Cloud Characterization Product
Regarding the algorithm development for the land degradation application at present we are focusing on the soil related matter. Hybrid classification techniques were selected for mapping areas affected by processes of erosion and indices for the characterization of the level of degradation of soils and surface texture; whereas, for natural vegetation land cover changes and functions, procedures and indexes were selected
• Level 2 products: HYP and PAN radiance and at ground reflectance products, geocoded and non geocoded
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for the characterization of the parameters associated with the level of coverage, conditions of stress, species composition, and degree of patchiness [4]. Concerning the agricultural applications, the activities were focused first on analyzing the bare soil properties on plowed agricultural fields’ images acquired by CHRIS-PROBA (ESA) and MIVIS hyperspectral sensors. Systematic sampling of the main soil properties and agricultural crops were performed on test sites near Rome (Italy). These data were used as input in the PLSR (Partial Least Square Regression) statistical model and so far, the best results were obtained for the estimation of the soil clay content (Fig. 1). This year the activities will be more focused on crop vegetation variables estimation (e.g. chlorophyll, LAI/biomass, fAPAR) and monitoring by hyperspectral satellite data. Finally, regarding the application of PRISMA for detecting, monitoring and managing of natural and anthropogenic hazards, we focused our efforts primary on the assessment of the damage severity (e.g., Damage Severity Index - DSI) and mainly on the effects of wildfires [2] induced on vegetated areas interested by a fire (Fig. 2). The project goal is also to develop specific indexes for land degradation (see e.g. in Fig. 3, soil erosion index - GSI) and for detecting and monitoring pollutants on soil and sea surfaces such as oil spills and heavy metals.
Fig. 1. Example of the estimation of the soil clay content for the Maccarese test site in Italy. Left, sampling scheme and, right, PLSR clay content estimation.
Fig. 3. Slope soil erosion evolution (2001-2012) by applying GSI (PRISMA) index to Hyperion data.
IV. CONCLUSIONS The paper reports the latest news in the development of the PRISMA space segment highlighting all aspects from the sensor and satellite design to the launch and satellite orbit. In particular, PRISMA is concluding the CDR, the schedule is still officially 2015, and PRISMA data simulator is going to be delivered by the industrial consortium. Calibration test sites are under evaluation and considered as opportunities for hyperspectral mission synergies and international partnerships, as the ISIS Working Group. Moreover, the paper describes the ongoing activities related to the SAP4PRISMA project and the methodological issues for retrieving geophysical and agro-environmental parameters for an improved modeling and understanding of biosphere and geosphere processes. The SAP4PRISMA project is in the third year of activity and level 3 first release products have been delivered to the Italian Space Agency (ASI). Moreover, soil characteristics by using PLSR and RK statistical analysis and crop vegetation biophysical properties using PROSAIL inversion are in progress. Exploitation of hyperspectral PRISMA data for land degradation application and DSI index for assessing post fires severity damages are under assessing. Calibration/Validation of the products is also foreseen. ACKNOWLEDGMENT The project is supported by the Italian Space Agency (ASI) with grant I/019/11/10
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S., Pignatti, Acito, N.; Amato, U., Casa, R.; de Bonis, R., Diani, M., Laneve, G., Matteoli, S., Palombo, A., Pascucci, S., Romano, F., Santini, F., Simoniello, T., Ananasso, C., Zoffoli, S., Corsini, G., Cuomo, V., “Development of algorithms and products for supporting the italian hyperspectral prisma mission: the SAP4PRISMA project”, Special Sessions: Spaceborne Imaging Spectroscopy Missions: Updates, and Global Datasets and Products, proceedings pp. 127-130, IGARRS 2012 22-27 July.
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