HYPERSPECTRAL IMAGING FOR REAL TIME LAND AND … · 2018-06-02 · base of the instrument design. Hereafter, the main ones are listed: 1. Optics and electronics to fit in a CubeSat

The 4S Symposium 2016 – S.S. Conticello et al.

HYPERSPECTRAL IMAGING FOR REAL TIME LAND AND VEGETATION INSPECTION

S.S. Conticello, P. Foglia Manzillo, C.N. van Dijk, N. Vercruyssen, M. Esposito1

M. Soukup, J. Gailis, D. Fantin, A. Jochemsen, C. Aas2

P.J. Baeck, I. Benhadj, S. Livens, B. Delauré3

M. Menenti, B.G.H. Gorte, S.E. Hosseini Aria4

M.D. Miranda, S.K. Mahalik5

1cosine measurement systems B.V., Oosteinde 36 2361 HE Warmond, The Netherlands

2Science [&] Technology AS, Forskningsparken Gaustadalléen 21, 0349 Oslo, Norway

3VITO, Boeretang 200, BE-2400 Mol, Belgium

4Delft University of Technology, Stevinweg 1, 2628 CN, Delft, The Netherlands

5 ESA-ESTEC/TEC – MMO, Keplerlaan 1, NL-2200 AG Noordwijk, The Netherlands

*[email protected]

Abstract

HyperScout is a hyperspectral nanosatellite payload operating in the VNIR with unprecedented low

mass and volume. The large field of view and the onboard intelligence deployed on a platform as

small as a 3U CubeSat enable a large variety of land and vegetation applications, for which cost

efficiency and timeliness are of foremost importance.

The system is extremely flexible and re-configurable in-orbit, resulting in a paradigm shift in the

space asset use. Different users may use the same sensor for different real time applications. The

same nanosatellite can support precision farming in Northern America and flood monitoring in

South-East Asia. The end data product can be continuously tuned to satisfy the needs of multiple

users, even over the same area of interest. HyperScout exploits the latest technological

developments in the fields of CMOS detectors, hyperspectral filtering, electronics miniaturization

and microprocessors. The result is a compact system, fitting in a CubeSat unit. HyperScout

overcomes the major CubeSat limitation, the downlink capability, by processing and downloading

L2 data products instead of the raw data.

HyperScout can be used as a single nanosatellite or within a larger mission. Major advantages are

obtained if used in constellation: 16 satellites allow for global coverage twice a day or single

coverage of a single country every 30 minutes.

1 INTRODUCTION: THE HYPERSCOUT CHALLENGE

It used to be generally acknowledged that NanoSat-accommodated instruments could not perform

hyperspectral operations, due to their limitations in terms of volume, power consumption,

computing and down-link capacity.

mailto:[email protected]


The HyperScout development has been carried out to demonstrate, instead, that leveraging on the

latest developments in optics, filtering, detection and computing technologies, it is actually possible

to perform hyperspectral sensing from a nanosatellite platform [1-2].

The development project, called HyperCube, had the goal of setting a new benchmark combining

hyperspectral state-of-art technology with the revolutionary CubeSat capabilities. The project was

performed under a ESA (European Space Agency) GSTP (General Support Technology

Programme) by a consortium lead by cosine measurement systems B.V. (NL), including VITO NV

(BE) and S[&]T AS (NO) and TU Delft (NL).

HyperScout operates in a push broom configuration and it is equipped with an On-Board Data

Handling (OBDH) system able to process in real time the data acquired. The objective is to enable

early warning by downloading the processed geophysical data products with coordinate

information, instead of raw data. HyperScout is conceived as a CubeSat payload, and thanks to its

small dimensions and high processing capability can be operated for a variety of applications,

ranging from vegetation monitoring to change detection.

It is a small, versatile and cost-effective instrument and its successful development, together with its

very good performance and wide range of promising potential applications, paves the way to its

launch as a commercial product. Thanks to the system re-configurability, the development of the

HyperScout presents a paradigm shift in the use of space asset: different user communities may use

the same space asset for different tasks, e.g. precision farming on Northern America, fire detection

in Australia, or the extension of a flood occurred in other areas of the globe.

In this paper, we present the instrument requirements and architecture as well as the main

applications. The operational approach, based on a new concept of the space asset use, is presented.

Possible mission scenarios are discussed, employing the instrument as single payload of a

NanoSatellite platform, as part of a larger mission and as a satellite constellation unit.

2 HYPERSCOUT REQUIREMENTS AND ARCHITECTURE

During the HyperScout development, many technological challenges have been faced to overcome

the severe limitation that had, so far, prevented a miniaturized hyperspectral imager for

nanosatellites from being developed. Figure 1 summarizes the design drivers which have been at the

base of the instrument design. Hereafter, the main ones are listed:

1. Optics and electronics to fit in a CubeSat Unit (1 L)

2. Time efficient optical alignment

3. Large fields of view

4. Delivery of end-user information

5. Real time information generation

6. Resilience to platform instability

7. Low power consumption;

8. Calibration with external bodies.


Figure 1: HyperScout design drivers

The main derived system requirements are summarized in Table 1.

Table 1: HyperScout main requirements

Parameter Value

Orbit 300 km to 600 km

Field of view 31º (Across track)

Ground Sampling Distance 80 m @ 600 km

Swath 336 km @ 600 km, 168 km @ 300 km

Number of spectral pixels > 600

Spectral range 450 – 900 nm

Spectral resolution 10 nm

Dynamic range > 8 bit

SNR 50 @ 300 Km

Mass < 2 kg

Volume <1 L

The HyperScout architecture can be conceptually divided among four subsystems:

1. Telescope

2. Focal plane array

3. Instrument Control Unit

4. On Board Data Handling.

The telescope comprises of three powered mirrors, which focus the radiance of the area in the FOV

on the Focal Plane Array (FPA), and the opto-mechanical system, which provide a stable support to

the optical and electronic units. A Linearly Variable Filter (LVF) is used to separate the different

wavelengths on the CMOS sensor, which is then read by the read out electronics (ROE).

The Instrument Control Unit (ICU) is the software and electrical interface to the spacecraft. It

distributes power, clocks, telemetry and commands between the units, controls the detector through

the ROE and merges the data acquired with the platform ancillary information creating L0 data,

which is then stored in the PL data storage subsystem.


The onboard data handling units (OBDH) host the processing algorithms that elaborate the data

from L0 to the L2A-L2B. The data is stored at every intermediate processing step. The final data

products are then down-linked via the SV communication system.

2.1 Assembly, integration and testing

A first engineering model of the HyperScout instrument has been integrated at cosine. Figure 2

reports two pictures of HyperScout as at the end of the assembly and integration phases.

A thorough testing campaign has been carried out to experimentally derive the main performance

figures of the instrument and compare them to the requirements. Table 2 reports a summary of the

measurements that have been performed on the telescope, grouping the measured parameters into

categories. In general, the instrument performs according to specifications for most of the

considered figures of merit, confirming that it will be possible to perform hyperspectral imaging

from a nanosatellite, i.e. making use of minimal resources.

A large number of test setups have been built at cosine premises, as well as test facilities at ESTEC

and at the Paul Scherrer Institute have been used. Figure 3 reports a picture of the HyperScout

system mounted in a two axes rotation stage, used in most of the performed tests. Figure 4 reports

two pictures of the interferometric setup, available at ESTEC premises, which has been used for the

measurement of the telescope optics MTF. Figure 5 reports a picture of the optical setup which has

been used to align the LVF on the detector. Figure 6 shows the HyperScout electronics, prepared for

the radiation test (high energy photon exposure) at Paul Scherrer Institute.

Figure 2: Pictures of the assembled HyperScout instrument.

Table 2: Overview of the measurements on the telescope.

Test Measurement

Optics Optics MTF

Geometric properties

Distortion

Focal length

Field of View

Entrance pupil diameter

System MTF

Spectral properties

Spectral response

Spectral range

Spectral resolution

Spectral straylight (due to filter)


Test Measurement

Radiometric properties

Relative radiometric response

Linearity, saturation, and dynamic range

Absolute radiometric response

Signal to noise ratio

Straylight (due to telescope)

Thermo/Vac Instrument performance under

thermo/vac

Figure 3: Picture of HyperScout mounted in a two axes rotation stage.

Figure 4: Picture of HyperScout in the interferometric setup used for Optical MTF measurement performed at

ESTEC laboratories.


Figure 5: Picture of the LVF – detector alignment setup. Figure 6: HyperScout electronics in the setup for the

radiation testing, performed at Paul Scherrer

Institute.

3 HYPERSCOUT APPLICATIONS

The definition of the applications and data products of the HyperScout instrument has been

achieved by means of a brainstorming session involving the instrument consortium and potential

end-users. The following applications have been selected for the onboard implementation:

1. Monitoring of vegetation conditions, drought (Figure 7)

2. Crop water requirements (Figure 8)

3. Fire hazard (Figure 9)

4. Delineation of flooded areas (Figure 10)

5. Land cover and land use change detection (Figure 11)

Figure 7: Drought Severity

Figure 8: Irrigated lands


Figure 9: MODIS-derived global burned areas (after

Frolking, 2010)

Figure 10: Globalmap of flood prone areas [3]

Figure 11: Global map of Land Cover [4]

The applications have been selected as they exhibit a worldwide relevance. Most of the applications

rely on spectral indices as proxy, thus minimizing computational load for producing the final

geophysical product. Some of used indexes are Normalized Difference Vegetation Index (NDVI),

Normalized Difference Water Index (NDWI), crop coefficients (Kc), Perpendicular Moisture Index

(PMI).

Land Cover and Land Use change detection algorithms represent a research subject of the Technical

University of Delft, and have been implemented for onboard processing. Spectral classification of

land cover and land use types has been a widespread application since the launch of Landsat 1.

However, apart from very simple classes, the accuracy of classification may result far from

satisfactory and ambiguous. The performance of classifiers can be significantly improved by

optimizing both the selection of spectral bands and of classifiers for a given set of classes in a

specific landscape. Onboard processing aims at detecting changes and processing of current spectral

data is performed within segments where a change is detected.

The important aspects for these applications are:

Detecting the changes that have occurred

Identifying the nature of the change

Measuring the area extent of the change

Table 3 reports the requirements that the considered applications put on the instrument and mission

parameters.

It is worthwhile remarking that the “modus operandi” of HyperScout is completely different from

that of larger, traditional, instruments which rely on the download of large amount of data. On the


contrary, HyperScout considers specific target areas for selected applications and performs an on-

board data processing for data reduction by scene. This results in the downlink of a very limited

amount of data, which only contain the piece of information which is relevant to the end user.

Table 3: Observation Requirements

Instrument

and mission

parameters

LC/LU change detection Fire

hazard

Irrigation

advice to

institutions

Irrigation

advise to

farmers

Flood

detection Forest Wetlands Urban

GSD 10–250 m 10-50 m 1-50 m 30-250 m 60-250 m 10-50 m 60-250 m

Area 31%

world's

land

<6%

world's

land

3%

world's

land

Forest's

land

33%

world's

land

33%

world's

land

Equals

wetlands

Spectral bands >20 <15 >15 <10 >20 >20 <15

Spectral

resolution 10 nm >20 nm >20 nm >20 nm 10 nm <10 nm >20 nm

SNR ~50 ~100 ~50 ~50 ~100 ~100 ~100

4 MULTI USER "MINDSET"

The HyperScout payload serves different applications, among which monitoring natural disasters

such as floods, forest fires and desertification. With such a system it will possible to:

1. Observe phenomena with high speed of change;

2. Delivery the information and its geo-location in quasi real-time;

3. Observing a set of phenomena within a single payload and satellite.

The onboard processing capabilities grant HyperScout an extremely flexible modus operandi. The

user is able to select the specific data product to be generated over a certain Region of Interest

(ROI). After the acquisition of the raw data, the parallel processing starts. While the spacecraft

moves forward and the HyperScout acquires a new raw data set, the OBDH performs L2A and then

L2B data generation. A pictorial description of the parallel acquisition/processing approach is

reported in Figure 12.

The L0-L2A data processing lasts approximately 30 seconds. The L2B data are subsequently

retrieved. The duration of the L2B processing step depends on the specific application. Estimates

for the L2B generation time for different applications are listed in Table 4.

A roadmap to further optimize the software has been derived, and when implemented processing

time is expected to go below the minute for most of the applications envisaged for HyperScout.

Table 4: Data products and onboard processing times

Application L2B Data Product Target onboard

processing time

1. Monitoring of vegetation conditions

(drought)

1.1. NDVI (t)

1.2. Mean NDVI (t)

1.3. NDVI anomaly at time t

40 s


Application L2B Data Product Target onboard

processing time

2. Crop water requirements 2.1. NDVI

2.2. WDVI

2.3. Kc

40 s

3. Fire hazard 3.1. Red reflectance

3.2. NIR reflectance

3.3. PMI

40 s

4. Delineation of flooded areas 4.1. Green reflectance

4.2. NIR reflectance

4.3. NDWI

5. Cover and Land Use Change 5.1. Image segmentation

5.2. SVM classification

5.3. Compressed reduced sets of wavelet

transformations of hyperspectral images

5.4. Spectral measurements of pre-loaded

segments: a list of segment id-s with

homogeneity indicators (yes/no)

according to a new image.

~60 s

~80 s

~60 s

~80 s

6. Reduced Spectral Configurations 6.1. Approximated/reconstructed bandset

6.2. Independent (optimal) bandset

6.3. Separable bandsets

~40 s

This versatile on board processing capability allows the generation of multiple data products over a

single ROI. Once generated, the data products are ready for download. HyperScout can therefore

provide quasi real time data to the users. Only a few minutes delay separates the acquisition and the

download of the data product. The instrument, together with a distributed net of ground stations, can

thus enable early warnings. If a satellite constellation with the instrument on board is considered, a

thorough land and vegetation inspection formation is obtained.

Figure 12 – Parallel processing and download strategy of the HyperScout instrument in operation

Orbit example

Given the extraordinary processing capability of HyperScout, each satellite orbit can therefore

result in a collection of multiple data products.

As an example, a polar orbit, passing over Eastern Africa and Europe, is considered (Figure 13). A

wide range of different applications are identified for the different ROIs, which are imaged along


the orbit path. The individual pairs of ROI and application are reported in Table 5.

Table 5: Example orbit regions of interest and applications

Region of Interest (ROI) Application

Mozambique Fire hazard, Floods

Tanzania Fire hazard, Floods

Uganda - Kenya Fire hazard, Change detection

Sudan Droughts

Egypt Floods, Droughts, Crops, Change Detection

Greece Fire hazard, Change Detection

Balkan regions Floods, Crops

Figure 13 – HyperScout ground track mission scenario

In the presented scenario, the instrument continuously acquires and the covered area results being

equal to 150.000 ha. The data products are ready to be downloaded 11 minutes after the acquisition

has been performed.

The users can even perform a reconfiguration of the data products per area of interest orbit by orbit,

dedicating more resources and observations to a specific event. HyperScout can also identify critical

areas and trigger a request for an in situ inspection, to be performed, for instance, with aircrafts or

drones.

4.1 Constellation scenario

The use of several instruments in a constellation of satellites can lead to the widest exploitation of

the HyperScout potentialities. In this paper, we present four different examples of constellations,

conceived to obtain different degrees of land coverage (worldwide, orbit – defined, regional or

single-country) at different revisit times, from twice a day down to twice an hour.

Constellation scenario 1: Europe twice per day

A first formation flight scenario has been considered. It requires 12 satellites to image the whole

Europe (excluding Russia, Ukraine and Iceland) twice a day, in the morning and in the afternoon.

Six satellites are sufficient to image the complete area of interest in slightly less than three hours.

Figure 14 reports the 2D coverage map for the considered six satellite constellation. Two orbits are

required to complete the image the complete area of interest. Figure 15 reports the current and


accumulated coverage as a function of time. The time curve of the latter parameter confirms that, if

the imaging process starts at 7 am, the complete coverage is achieved slightly before 10 am. It is

worthwhile remarking that the six satellites almost equally contribute to the coverage of the region

of interest, resulting in a balanced use of the available resources.

Analogous results are obtained if a second, identical, constellation is considered for imaging the

same area of interest for a second time during the same day.

Figure 14: 2D coverage map. The pink area is entirely imaged by six sensors over two orbits.

Figure 15: Current (red) and accumulated (cyan) coverage as a function of time for a six satellite formation.

Constellation scenario 2: Orbit segment four times per day

A constellation of four HyperScout instruments can be used to image the same orbit four times a

day. As already discussed in the previous sections, it is possible to define orbits such that several

regions of interests can be observed during one revolution for multiple applications. Table 5

indicates different ROIs in Eastern Africa and Eastern Europe which can be imaged along the same

orbit.

Another orbit of interest could include the The Hague/Rotterdam urban area and the Saar Delta,

relevant for land use applications, the Dhoukkala area (Morocco), relevant for crop monitoring, the

Northern Burkina Faso, relevant for fire detection, the Zambesi area, relevant for flood detection.

Constellation scenario 3: Worldwide twice per day


A constellation of HyperScouts could also be used to obtain full worldwide coverage twice a day.

From a Sun synchronous orbit, at an altitude of 600 km, (swath on ground of 340 x 150km) a total

of 16 HyperScouts would be required to achieve full global coverage. Figure 16 reports the 2D

coverage maps for this formation scenario.

Figure 16 – HyperScout Global coverage, twice a day revisit time

Constellation scenario 4: Single country every half an hour

An extremely interesting possibility is to consider a constellation in which HyperScout can be

deployed and that is capable of obtaining an extremely high revisit time, up to twice per hour.

A constellation of 16 satellites could generate hyperspectral images and data products for a given

country daily every 30 minutes (9.00 am to 4.30 pm). Figure 17 indicates how the swath of a single

instrument, if operated at an altitude of 600 km, is comparable to the surface of the Netherlands,

while Figure 18 reports a 2D map with the orbits of 16 satellites required to image it twice an hour.

Figure 17: Swath of HyperScout from 600 km over the Netherlands

4.2 In-Orbit Demonstration and HyperCrowd

The next step in the instrument development is testing its functionalities and performance in space.

Currently, an in-orbit demonstration (IOD) of the HyperScout instrument is planned. cosine is

delivering the payload fling model at the end of the year 2016, while the launch is scheduled for

early 2017. HyperScout will be mounted on board of a 6U platform, which will orbit the Earth at

540 km altitude. The IOD will enable the evaluation of the data products which HyperScout is able


to generate for different applications. The expected successful conclusion of the IOD will then

allow the launch of HyperScout as a real commercial product. The instrument unique capability of

generating different data products on the same region of interest results in the possibility of sharing

the space asset among different users who might jointly contribute to the manufacturing and launch

expenses. The HyperCrowd is the crowd-funding approach that will be proposed to the space

market.

Figure 18: – HyperScout Netherlands coverage, 30 minutes revisit time

4.3 Operations on large platforms

The possibility of employing the HyperScout instrument on board large satellites has been also

preliminary evaluated. With its large swath, HyperScout can be employed for change detection and

early warning applications and therefore can be complementary to a high resolution instrument. It

can be used for identifying the locations of interest in real time. At the moment the spacecraft

platforms which are being considered are the Italian Space Agency (ASI) PRISMA (PRecursore

IperSpettrale della Missione Applicativa) medium resolution hyperspectral instrument (GSD of

30 m, swath of 30 km) and OPSIS (OPtical System for Imaging and Surveillance) with a GSD

<1 m.

Figure 19: The CAD model of PANORMA showing the 4 HyperScouts.

Multiple HyperScout instruments can be also combined together to enlarge the instrument field of

view and spectral range. The quad configuration has been named PANORAMA (Figure 19) and it

has been conceived for being used as a viewfinder in the VIS-NIR-SWIR for STREEGO, a high


spatial resolution instrument in VIS-NIR and with GSD in the meters range and consequently with

limited FoV [5]. The idea is to couple the two instruments on the same platform, using

PANORAMA to detect real time anomalies and to point STREEGO on these anomalies for higher

resolution observations. This is possible because the hyperspectral instrument is conceived to have a

pre-stored Earth map on the on-board computer that is used as comparison during observations, so

that whenever the land looks different an alert is raised.

5 CONCLUSIONS

HyperScout, a miniaturized hyperspectral imager, has been successfully manufactured and tested.

Taking advantage of the most recent technology developments in CMOS detectors, hyperspectral

filtering, optical manufacturing and materials and state-of-art level 2 algorithms, the unprecedented

possibility of performing hyperspectral sensing from a nanosatellite has been enabled.

The instrument performance is sufficient to enable a very broad range of applications, ranging from

water and vegetation remote sensing, to fire detection, early warning, precision farming, flood

detection. The on-board processing capabilities allow the instrument to generate the data products

while imaging, minimizing the delay between acquisition and data downlink, resulting in quasi-real-

time information.

Thanks to the re-configurability of the system, the development of the HyperScout presents a

paradigm shift in the use of space asset: different user communities may use the same space asset

for different tasks, e.g. precision farming on Northern America, fire detection in Australia, or the

extension of a flood occurred in other areas of the globe.

HyperScout, being a small, cost-effective and highly reconfigurable payload, can be effectively

used in a large variety of missions, ranging from large-scale, as support instrument to larger

payloads, to small scale, providing commercially valuable data products to a broad end-user

community.

As the cost of one HyperScout instrument is extremely low if compared to that of conventional

instruments, the use of satellite constellations could result economically affordable with an

extremely valuable performance. For example, 16 satellites could suffice to image the whole Earth

surface twice a day or to image a limited area of interest, e.g., a country such as the Netherlands,

twice an hour during the whole day.

6 ACKNOWLEDGMENTS

The authors wish to acknowledge: Mr. Luca Maresi and Mr. Alessandro Zuccaro Marchi of ESA

ESTEC/MMO, for the valuable support and commitment that made possible to build the first

Engineering Model; Mr. Mathieu Breukers of VDL ETG Research B.V. for the excellent work in

manufacturing the HyperScout optics; The Netherland Space Office (NSO), the Belgian Science

Policy Office (BELSPO) and the Norvegian Space Centre (NSC) for funding the project through the

ESA GSTP program.


7 REFERENCES

[1] Esposito, M. et al, “HyperCube - The intelligent hyperspectral imager,” 2015 IEEE International

Workshop on Metrology for Aerospace, Benevento, Volume: CFP1532W-USB.

[2] Soukup, M. et al, “HyperScout: Onboard Processing of Hyperspectral Imaging Data on a

Nanosatellite,” Proc. 4S conference 2016, Malta.

[3] NASA Earth data, https://earthdata.nasa.gov/ World Resources Institute, Aqueduct,

http://www.wri.org/our-work/project/aqueduct

[4] ESA 2010

[5] Ferrario, I. et al, “HyperStreego: reactive payload”, Proc. 4S conference 2016, Malta.

Documents

HYPERSPECTRAL IMAGING FOR REAL TIME LAND AND … · 2018-06-02 · base of the instrument design. Hereafter, the main ones are listed: 1. Optics and electronics to fit in a CubeSat