Effect of satellite formations and imaging modes on global albedo estimation

Nag, Sreeja; Gatebe, Charles K.; Miller, David W.; Weck, Olivier L. de

doi:10.1016/j.actaastro.2016.04.004

Cited by 17 publications

(30 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…More fuel allows for faster initialization. As confirmed in Nag et al (2016b), the monthly ∆V per satellite to maintain the formation can be as 15 low as 0.5 m/s, and more than 80% overlaps between the ground spots are guaranteed for 0.5…”

mentioning

confidence: 69%

“…For a given altitudeinclination combination, previous studies (Nag et al (2015)) have compared a total of 1,254 architectures containing three to nine satellites in terms of surface BRDF error, averaged (root mean square) over the simulation day. The only orbital difference among the satellites are in their right ascension of ascending node and mean anomaly, because these were found to be maintainable over a year with propellant available within small satellite of commercial capability (Nag et al (2016b)). …”

Section: Orbit Design and Systems Engineeringmentioning

confidence: 99%

“…Our proposed 20 formation requires that all satellites point to the same target at approximately the same time, which needs agility and consistent attitude control. Simulation studies have demonstrated that it is possible to maintain the orbits and orientation of small satellites in such a formation, using commercially available propulsion and control systems (Nag et al (2016b)). …”

Section: Systems Engineering Modelmentioning

confidence: 99%

“…Payload pointing strategy 2 in section 2.1 is used, i.e. the nadir pointing satellite changed dynamically based on an algorithm documented in Nag et al (2016b), because this imaging mode was found to produce the least surface BRDF estimation errors without compromising spatial or global coverage. It is assumed that algorithms are run and decisions made in ground stations and communicated to the satellites during daily overpasses.…”

Section: Orbit Design and Systems Engineeringmentioning

confidence: 99%

“…For the earth, BRDF is typically symmetric about the solar azimuth angle, so that φ s and φ v can be condensed to φ = φ s − φ v (Knobelspiesse et al (2008)), which was what was used here. The algorithm used to determine the optimal formation flight architectures, which assessed their ability to determine 5 BRDF (Nag et al (2015)) or any BRDF dependent product (Nag et al (2016b)), did take the asymmetric azimuth nature into account. In practice, observations are often expressed as a unitless quantity (reflectance, see section 3.3) that has been integrated over solar geometries and represents a finite view solid angle.…”

mentioning

confidence: 99%

See 4 more Smart Citations

Remote sensing of aerosols with small satellites in formation flight

Knobelspiesse¹,

Nag²

2018

Preprint

Self Cite

View full text Add to dashboard Cite

Abstract. Determination of aerosol optical properties with orbital passive remote sensing is a difficult task, as observations often have limited information. Multi-angle instruments, such as the Multi-angle Imaging SpectroRadiometer (MISR) and the POlarization and Directionality of the Earth's Reflectances (POLDER), seek to address this by making information rich multi-angle observations, which can be used to better retrieve aerosol optical properties. The paradigm for such instruments is that each angle view is made from one platform, with, for example, a gimbaled sensor or multiple fixed view angle sensors. 5This restricts the observing geometry to a plane within the scene Bidirectional Reflectance Distribution Function (BRDF ) observed at the top of the atmosphere (TOA). New technological developments, however, support sensors on small satellites flying in formation, which could be a beneficial alternative. Such sensors may have only one viewing direction each, but the agility of small satellites allows one to control this direction and change it over time. When such agile satellites are flown in formation and their sensors pointed to the same location at approximately the same time, they could sample a distributed set 10 of geometries within the scene BRDF . In other words, observations from multiple satellites can take a variety view zenith and azimuth angles, and are not restricted to one azimuth plane as is the case with a single multi-angle instrument. It is not known, however, if this is as potentially capable as a multi-angle platform for the purposes of aerosol remote sensing. Using a systems engineering tool coupled with an information content analysis technique, we investigate the feasibility of such an approach for the remote sensing of aerosols. These tools test the mean results of all geometries encountered in an orbit. We 15 find that small satellites in formation are equally capable as multi-angle platforms for aerosol remote sensing, as long as their calibration accuracies and measurement uncertainties are equivalent. As long as the viewing geometries are dispersed throughout the BRDF , it appears the quantity of view angles determines the information content of the observations, not the specific observation geometry. Given the smoothly varying nature of BRDF 's observed at the TOA, this is reasonable, and supports the viability of aerosol remote sensing with small satellites flying in formation. The incremental improvement in 20 information content that we found with number of view angles also supports the concept of a resilient mission comprised of multiple satellites that are continuously replaced as they age or fail.

show abstract

mentioning

confidence: 69%

Section: Orbit Design and Systems Engineeringmentioning

confidence: 99%

Section: Systems Engineering Modelmentioning

confidence: 99%

Section: Orbit Design and Systems Engineeringmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Remote sensing of aerosols with small satellites in formation flight

Knobelspiesse¹,

Nag²

2018

Preprint

Self Cite

View full text Add to dashboard Cite

show abstract

Applying autonomy to distributed satellite systems: Trends, challenges, and future prospects

Araguz

Bou-Balust

Alarcón

2018

Systems Engineering

View full text Add to dashboard Cite

While monolithic satellite missions still pose significant advantages in terms of accuracy and operations, novel distributed architectures are promising improved flexibility, responsiveness and adaptability to structural and functional changes. Large satellite swarms, opportunistic satellite networks or heterogeneous constellations hybridizing small-spacecraft nodes with high-performance satellites are becoming feasible and advantageous alternatives requiring the adoption of new operation paradigms that enhance their autonomy. While autonomy is a notion that is gaining acceptance in monolithic satellite missions, it can also be deemed an integral characteristic in Distributed Satellite Systems. In this context, this paper focuses on the motivations for system-level autonomy in DSS and justifies its need as an enabler of system qualities.Autonomy is also presented as a necessary feature to bring new distributed Earth observation functions (which require coordination and collaboration mechanisms) and to allow for novel structural functions (e.g. opportunistic coalitions, exchange of resources or in-orbit data services).Mission Planning and Scheduling frameworks (MPS) are then presented as a key component to * Corresponding author. E-mail addresses: {carles.araguz, elisenda.bou, eduard.alarcon}@upc.edu 1 implement autonomous operations in satellite missions. An exhaustive knowledge classification explores the design aspects of MPS for DSS, and conceptually groups them into: components and organizational paradigms; problem modeling and representation; optimization techniques and metaheuristics; execution and runtime characteristics; and the notions of tasks, resources and constraints. This paper concludes by proposing future strands of work devoted to study the tradeoffs of autonomy in large-scale, highly dynamic and heterogeneous networks through frameworks that consider some of the limitations of small spacecraft technologies.

show abstract