In the scope of the FLEX earth explorer mission, a major key element is the atmospheric model to simulate the propagation of the faint red light emitted by plants photosynthesis up to the satellites sensor. The measure of this sun induced fluorescence is based on the oxygen atmospheric absorption lines at 760 nm and 685 nm. However the same absorption lines will erase most of the signal while it travels upwards through the atmosphere. To model the atmospheric absorption in different layers of the atmosphere, accurate hyperspectral measurements at different altitudes are necessary.
To assess this open question, a high resolution spectrometer with specifications similar to the FLEX mission was developed as a payload for airborne missions. This AirFloX is an automatic payload with large data storage, variable field of view, low weight and small energy consumption. Still the instrument features a thermo-regulated sensor to maintain stable measurements conditions.
To approach the dense lower atmosphere, a special unmanned fix wing aircraft was designed and manufactured, capable of carrying the AirFloX up to 4 km. The circular flight pattern, combined with a stabilizing platform is aimed to measure a small homogenous surface below the flying platform from increasing altitudes. We present the efforts in design and development of payload and unmanned platform as well as insights in the running survey mission and its results. We further discuss possible future deployments on very high altitude platforms and their impact on the atmospheric modelling for the FLEX mission.

NASA Earth Science and Aeronautics researchers have been involved in development and use of High Altitude Long Endurance (HALE) unmanned aircraft systems (UAS) since the 1990’s. The NASA Environmental Research Aircraft Sensor and Technology Program (ERAST) demonstrated the promise of HALE aircraft for providing observations while also proving the importance of triple-redundant avionics to improve system reliability for large unmanned aircraft. Early efforts to develop an operational HALE capability for earth observations languished for nearly two decades owing to insufficient solar panel efficiency, battery power density, and light-weight, yet strong, materials. During this time NASA researchers focused on using the Global Hawk to demonstrate the utility of providing diurnal measurements over severe storms (ie. HS3) and to track stratospheric water vapor transport (ATTREX). Recent significant commercial investments are now leading to the realization of a long-held goal of week- to month-long sustained observations and measurements from the stratosphere. In addition to a historical review of NASA use and interest in HALE aircraft, this paper will present current concepts for exploiting current and planned HALE aircraft capabilities including in situ characterization of atmospheric composition and dynamics as well as imagery collection. NASA researchers anticipate HALE will provide a useful means to test smallsat instruments and components. Observations from HALE-based instruments might also provide useful gap-filler observations to flagship satellite missions where the repeat time doesn't allow for measurements of quickly changing phenomenon. HALE will likely also provide measurements and communications relay to facilitate other aircraft in multi-aircraft campaigns. We will also report on progress towards a NASA-funded flight test planned for summer 2019 of a solar-electric vehicle designed to carry 7kg (15lbs) for 30 days at 20km altitude.

The European fleet of Earth Observation satellites, i.e. Earth Explorer, meteorological and Copernicus missions, are providing information to various communities on global and regional scales. However, they have only limited capability to provide information on a local scale with high observation frequency and spatial resolution.
Currently, HAPS platforms, current and under development, fall into two broad categories: heavier-than-air (aircraft like) and lighter-than-air, which may be further divided into hybrid (i.e. airship) and free flight (i.e. balloons). Both categories have their pros and cons. For instance, free flight balloon approach may appear to offer simplicity but balloons are difficult to control or to keep on station. Moreover, hybrids approaches could offer a larger payload but they are more sensitive to wind than a heavier than air vehicle. However, both categories offer higher revisit times and higher resolutions than GEO and LEO satellites. Therefore, HAPS have the potential to bridge the gap between satellites and ground based observations.
In this paper, we assess operational scenarios for HAPS missions in support of ESA Earth Observation Satellites. Thus, we identify synergies between a large spectrum of current/future EO European missions and observations capacity supported by a HAPS platform. Based on these synergies and on the operational scenarios, end-to-end HAPS mission requirements are defined. Satellite-HAPS synergy scenarios have been elaborated leveraging on users’ needs, EO services generation and delivery, HAPS technologies, EO instruments, and ESA and European EO missions.
In order to identify which synergies between HAPS and EO satellite missions would be possible and of greater interest, the EO satellite mission requirement documents were analysed and gaps between users’ needs and mission performances were assessed. We performed an extensive review of existing and future HAPS world-wide solutions. In addition, a review of EO instruments enabled answering the question “what kind of EO payloads could be deployed on HAPS?”.
We consolidated the scenarios by consulting relevant stakeholders and specific user communities. Thus, we gathered user requirements on several issues as observation needs (acquisition delay, revisit frequency…), product’s needs, description of applications and services to be provided, information on how they proceed today to generate value-added, global impact of the application to be developed or enhanced.
Finally, we defined the geophysical and observations requirements for the Satellite-HAPS synergy scenarios, and define how the envisaged payload and the HAPS system should be designed and operated to manage them. The HAPS mission requirements document therefore outlines the identified user requirements and transforms these requirements into traceable mission requirements specifying the observational needs and quantitative requirements in terms of geographical coverage, revisit time, spectral, radiometric and geometric performance.

Spaceborne and airborne earth observation already provide a valuable role in forest fire monitoring, maritime surveillance and border surveillance services. However, gaps remain between operational service capability and user requirements. With the emergence of “New Space”, earth observation is increasingly being known to encompass other technologies such as HAPS, which will further enrich the information currently sourced from satellites, manned aviation and conventional drones. High Altitude Pseudo Satellites (HAPS) have significant potential to overcome observational constraints currently encountered with existing technologies delivering these services. The precise (or potential) capabilities of a HAPS platform depend on the platform and approach taken, i.e. fixed wing, free flight balloon or airship, but in general HAPS offer flexibility and persistence.

We review the benefits of the integration of HAPS-derived data into three service areas: (1) forest fire monitoring, (2) maritime surveillance, and (3) border surveillance - those services where there is a need for 24-hour monitoring, high spatial resolution, large coverage area, and remote areas with little or no ground infrastructure. Each of these three service themes create challenges for local and national agencies to monitor and manage whilst the need for an improved and integrated monitoring policy increases.
• Cost of fire protection and suppression is increasing with the impacts of climate change;
• Illegal, unreported and unregulated (IUU) fishing accounts for up to 20% of all wild marine fish caught;
• Criminals are increasingly using oceans for trans-national organised crime;
• Illegal immigration and smuggling of both people and illicit goods over national boundaries has experienced influxes in recent years.
These three service areas have been identified as deriving significant benefit from a future HAPS-based approach to monitoring, complementing those services currently achievable from the combination of established space and airborne platforms together with ground-based observational infrastructure.

We will share findings from the ‘HAPS-enabled services complemented by satellites’ study (ESA Contract No. 4000124383/18/NL/CLP) in which stakeholder consultation paved the way for a better understanding of where challenges lie in delivering these three services, a list of user requirements was developed, in addition to an understanding of where HAPS can provide a complementary capability. The user community helped identify requirements that should be addressed to align existing operational capabilities with end user needs. There is a high level of coherence between requirements from different end users and applications. This presentation will provide an overview of each service scenario, and the associated key acceptance criteria.

HAPS has significant potential to offer valuable capabilities that will complement and augment existing services, and thus the development of synergies between data sources should be considered key to optimise the performance of operational services.

In the last two decades, observations from polar orbiting satellites such as GOME, SCIAMACHY, OMI and Sentinel-5P (TROPOMI) have provided increasingly detailed and accurate information about the global distribution of air pollutants, its sources, seasonal variability and long-term trends. Air pollution is however not only a global issue, but - in contrast to climate change - first of all an issue on the city scale. On this scale (say 100x100m) there is an observational gap that will not be covered by satellite missions in the near future and it is a wish frequently expressed by city environmental authorities to fill this gap in order to facilitate better monitoring and political decision making w.r.t. the mitigation of societal problems related to air quality.

The Spectrolite breadboard instrument that has been developed by TNO has demonstrated the ability to measure tropospheric nitrogen dioxide (NO₂) columns at a high spatial resolution: effectively 30x30m from an airborne platform at 3km altitude (AROMAPEX campaign Berlin, 2016). Such a lightweight (8kg) instrument is particularly suitable for deployment from a HAPS platform.

Observations from a HAPS platform will provide a unique opportunity for cities / city regions to monitor concentrations (and/or vertical columns) and derived emissions of air pollutants at high spatial and temporal resolution during the course of one day or a series of days. An intensive campaign of several cloud free days will provide a reference picture of the air quality of a city (region). Future revisits of the platform allow for the monitoring of effectiveness of mitigation measures.

In addition, HAPS air quality data sets will provide excellent validation data for regional and city scale air quality models and satellite observations from polar orbiting or geostationary satellites. In turn, such models are an essential prerequisite for obtaining HAPS air quality products with sufficient accuracy to discriminate local sources from the city background.

The potential of High Altitude Pseudo-satellites (HAPS) for Earth Observation (EO) is widely accepted nowadays. In contrast to the advantages of closeness with respect to satellites, and endurance and stability with respect to unmanned aircrafts, these systems pose new constraints to instruments, communication channels, and data processing chains.
The present work trades-off different alternatives to produce persistent high-resolution observations by means of passive sensors, which probably will be the first in being integrated into HAPS. The instrument requirements are taken from target applications in the fields of:
- Security: surveillance of wide areas and tracking of suspicious activities
- Emergency management: prevention, real-time progress, actuations, means and recovery
- Human activity management: urban and coastal areas, infrastructures and traffic
The analysis includes comparisons relative to scanning mechanisms and monolithic multi-camera designs, radiometric budgets for visible and infrared channels, optical design solutions, detector options, on-board compression, and processing and environmental protections. All that with a target payload mass of 5 kg and 300 W consumption, compatible with the first prototypes of HAPS to be soon available. A baseline design is provided together with the results of stratospheric balloon tests executed on engineering models.
A performance study case has been developed for the particular case of the island of Fuerteventura, the UNESCO Biosphere Reserve in Canary Islands. With a maximum slant angle of 45 deg, three HAPS can continuously cover the 1700 km² of its territory. The towns (150000 inhabitants, very concentrated in few locations) and the coastline can be monitored for conservation, illegal activities and management of the touristic activity, the major economic activity. The proposed concept is compared to the current data sources and applications to highlight the value of HAPS as local, dedicated, customisable and affordable observation platforms. The feedback of the Local Administration is also part of the study.