Planet operates a fleet of more than 200 satellites, which represents the largest fleet of Earth observation satellites in the history of humankind. Having pioneered the concept of agile aerospace, we constantly upgrade the capabilities of our satellites, which have undergone multiple design iterations. This results in an operational fleet which contains different hardware generations onboard. In terms of image quality, this requires a software processing pipeline capable of handling these differences to ensure overall image quality stability. This is particularly pertinent as the fleet includes 21 high resolution satellites with a system design that is completely different and indisputably more complex than the rest of the satellites.

As a disruptive market player and as part of its agile aerospace model, Planet has accepted and embraced this quality assurance challenge. Multiple teams within Planet are involved in tackling this issue, starting from system design and the manufacturing process, through payload maintenance, sensor and pixel calibration, and ending with an assessment along the software life cycle of the processing pipeline generating the ortho products. Over the last three years, the customer perspective has also been integrated into the quality assurance process, adding a final quality control step after the product processing pipeline has been completed

Planet’s Automated Quality Assurance (AQUA) team focuses on imagery geopositional accuracy. For this, the team has built a separate processing pipeline reviewing product quality through sampling from a millions-per-day product stream. In this session, the AQUA team will present its separate production pipeline which continuously measures key performance indicators of Planet’s fleet. This is done using non-Planet resources and software for example by employing independent reference imagery over a world spread set of test sites and then using the PCI Geomatica software to find checkpoints from Planet’s ortho products against the reference data set. The usage of independent resources in this process is intended and crucial in order to measure the product quality in such a way that the results can be reproduced by anyone outside Planet.

For over 40 years, European Space Agency (ESA) Earthnet Programme has played a significant role as part of ESA’s mandatory activities, providing the framework for integrating non-ESA missions, i.e. Third-Party Missions (TPM), into the overall ESA Earth Observation (EO) strategy. The Earthnet Programme also allows European users access to a large portfolio and promotes the international use of the EO data. In agreement with the Earthnet Programme objectives, ESA aims to foster cooperation and collaboration with not only other national space agencies, but also commercial mission providers.

There has been an increase on the number of commercial bodies using their own satellite systems for data derivation, thanks to their low cost, and establishing in this way business models. Due to the availability of these new missions, the Earthnet Data Assessment Pilot (EDAP) was created to assess the quality and the suitability of TPM and EO ESA missions, and to establish dialogue with various mission providers for improving the overall coherence of the EO systems. The EDAP activities aim at providing various clusters of expertise to perform an early data quality assessment of existing or future EO missions from national or commercial providers, which may potentially become TPMs within ESA’s Earthnet Programme.

In the context of Very High Resolution data, driven by user applications and innovative data processing technologies, most of data providers are now proposing a new generation of Earth Observation products. Post-processing algorithms are now widely promoted in order to increase image spatial resolution pursuing the objective to improve detection/identification/characterization of objects with risk of losing radiometric fidelity. Similarly, new space technologies enable the acquisition of remote sensing video data dedicated to motion tracking. To address these new products, EDAP team is working on the evolution of methodologies dedicated to the evaluation of image quality. Also, the first part of this talk is intended to review image quality metrics (Signal to Noise Ratio (SNR), Modulation Transfer Function) and underlying methodologies. With the perspective of EDAP quality control team, accuracy results from different missions (Black Sky, SkySat, Maxar) will be shown and discussed.

From these operational activities emerged some calibration/validation needs, partially fulfilled with the existing infrastructures. To overcome these shortcomings, several concepts are now promoted. In this presentation, a particular attention will be paid to image quality test site requirements and within this scope how the ESA Cal/Val park initiative might become an important tool for the community.

Long-Term Trends in VHR Satellite Data Quality as measured by JACIE

The Joint Agency Commercial Imagery Evaluation (JACIE) effort was formed in 2000 by three United States government agencies to evaluate the quality and potential utility of newly launched commercial systems, beginning with Ikonos. The methods and results of these independent assessments of data quality were shared with the vendors and resulted in improved data quality. These results were also shared publicly through the annual JACIE workshops that have been held since 2001. Over the course of more than twenty years, JACIE has grown to six federal agencies in the U.S. continuing to leverage their unique resources to characterize remotely sensed data and present these results to the remote sensing community.

JACIE agencies have assessed and reported the quality of over twenty high- and very high-resolution satellite systems. The results of these various assessments are reviewed in this presentation and any trends or variances in the results noted. We will also present the methods used to assess the geometric, radiometric, and spatial quality of data, the strengths and weaknesses of the various methods in these assessments, and how the assessment processes have matured over the years of JACIE analyses.

This presentation will conclude with some brief speculations as to what past trends and current activity indicates for future directions and needs in the remote sensing community.

In its first year of commercial operations, Capella Space has dedicated a significant amount of effort into the characterization of the quality of the VHR SAR data collected by its satellites. As the satellite constellation has grown steadily throughout 2021, Cal/Val tests are carried out continuously, during satellite deployment, as well as during commercial operations.

Capella Space satellites are capable of collecting VHR SAR imagery in three different imaging modes: Stripmap (with GRR of 1.2 m), Sliding Spotlight (GRR 1.0 m) and Spotlight (GRR 0.5 m). The data is delivered in three formats: Single-look Complex (SLC), Geocoded Ellipsoid-Corrected (GEC) and Geocoded Terrain-Corrected (GEO). For the geocoded (GEC and GEO) Sliding Spotlight and Spotlight products, multi-looking is applied to reduce speckle noise and enhance image quality, resulting in very high-quality SAR imagery ready for analysis for use cases like Geo-Intelligence, Agriculture, Urban Monitoring, DEM generation and so on.

Capella operates satellites in three orbital planes, 45 degrees inclined, 53 degrees inclined and 97 degrees sun-synchronous. The satellites in inclined orbits allow customers to collect SAR data with different look directions than from standard sun-synchronous orbits. Capella has developed their Console web-portal and API, though which users can search archive data, order or task new satellite collects directly. This system is set to run automated, without the need for any human in the loop.

Capella has been participating in the Earthnet Data Assessment Pilot (EDAP) project, which is responsible for assessing the quality and suitability of candidate missions being considered for the Earthnet Third Party Missions (TPM) for ESA. As part of this campaign, Capella has delivered a large SAR data stack for validation in October 2021. The validation focused on the following aspects, analyzed with SLC data: a) verification of the impulse response function (IRF), b) estimation of geolocation accuracy, c) estimation of Noise-Equivalent Sigma Zero level (NESZ level), and d) verification of Elevation Antenna Pattern (EAP).

In this presentation the results from the EDAP analysis will be presented, as well as future plans for continued Cal/Val activities at Capella.

Synthetic Aperture Radar (SAR) data contains a very high level of informative content that allows the application to be used in many domains. Image quality is affected by various artifacts that can limit their use. Important classes of artifacts are the range and azimuth ambiguities.
The first approach to reduce the ambiguities is to design the SAR system by selecting the antenna size and the PRF accordingly.
Unfortunately, the proper design may not be in line with the requirements of modern micro-SAR platforms. New SAR satellite constellations are equipped with smaller antennas compared to their predecessors, imposing constraints that restrict conventional suppression of the ambiguities.
The range and azimuth ambiguities affect all the pulsed radar systems, due to the aliasing generated by the periodic signal sampling.
An inherent consequence of the pulsed operation of SAR is the range ambiguity that is caused by the echoes of the previous and latter transmitted pulses scattered from undesired regions.
The azimuth ambiguities are caused by finite sampling and sidelobe backscattering contamination from adjacent pulses. This is because the SAR spectrum is not strictly band-limited, and the signal band is contaminated by ambiguous signals from adjacent spectra.
In this paper, we present the techniques and algorithms used by ICEYE to detect and suppress ambiguities.
The range ambiguity suppression methods are focused on applying waveform diversity and suppressing the residual ambiguity by dual focusing. The basic idea behind waveform diversity is to gain the ability to mark the pulses. The system must be able to transmit signals with different marks and to identify the scattered signals respectively. There are at least three different waveforms proposed in the literature: Up and Down Chirps, (UDC), Azimuth Phase Coding (APC) and Cyclic Frequency (CF).
In most cases, the nadir and range ambiguity suppression that is achieved with UDC waveform diversity is sufficient to extract a high-quality SAR image. However, the energy is not suppressed but smeared in the range direction and may result in range stripes for a target that has a strong backscattering. Another problem is with the extended targets at the ambiguous regions. The uncompressed summation of adjacent scatterers of an extended target may result in a strong reflectivity. To overcome this problem, post-processing algorithms that are based on dual focusing techniques are proposed. In these techniques, raw data is focused according to the ambiguous region. The image of the ambiguous region is then thresholded and complex data is suppressed; so the higher backscattering is assumed to represent ambiguous targets although a useful signal may also be lost. The last step is defocusing back to raw data and then focusing the raw data according to the unambiguous region parameters.
The first algorithm is based on the waveform diversity concept. UDC and APC are combined to suppress not only the nadir but also the range ambiguity. For this purpose, the ambiguity number of the nadir is estimated and the waveform is defined accordingly. The post-processing algorithm steps are based on a double dual focusing technique that suppresses not only the nadir but also the range ambiguity targets. A nadir detection algorithm is developed to achieve suppression of nadir while preserving the desired signal. The proposed algorithm follows with the range ambiguity detection method that relies on a combination of Ordered Statistics (OS) CFAR and CA CFAR. The experimental results show that the algorithm has promising results for suppressing the range ambiguity. In addition, the ambiguous image is extracted to verify how well the nadir and the ambiguous features are suppressed.
In Figure 1 the results of the proposed method are presented. The first image is extracted without waveform diversity. In the second image, a combination of UDC and APC is applied. The third image is the result after a dual focusing technique is applied to suppress the nadir. The 4th image is the final image that the range ambiguity is also suppressed. The last image presents an ambiguous image. The validation of the proposed method will be given in the final version of the paper.


(a) (b) (c) (d) (e)
Figure 1. SAR Images: a) Without waveform diversity. b) With waveform diversity c) With waveform diversity and nadir suppression d) With Waveform diversity and nadir and range ambiguity suppression. e) Range Ambiguous image

About the azimuth ambiguities, ICEYE developed two algorithms for ambiguity detection and suppression.
The proposed ambiguity detection algorithm to detect the ambiguities is named Phase Variant Analysis (PVA). The PVA algorithm uses the combination between a dedicated subaperture filtering and the derivative phase information to decouple the ambiguity from the main signal reducing the false alarms due to the range ambiguities and strong targets, as occurs in urban areas.
The proposed algorithm to suppress the ambiguities in SLC data is named Selective Doppler Frequency Suppression (SDFS). It is based on the detection of the ambiguous azimuth and range variant energy, that can be decoupled from the main signal in the Doppler Spectrum. The algorithm works iteratively to detect and filter all the ambiguous signatures in the Doppler spectrum.
The advantages of the aforementioned algorithms are the processing speed and the independence of specific models, as the antenna pattern.

The Earthnet Data Assessment Pilot (EDAP) is a project that is responsible for assessing the quality and suitability of candidate missions being considered for the Earthnet Third Party Missions (TPM). For over 40 years ESA's Earthnet Programme has played a significant role as part of ESA's mandatory activities, providing the framework for integrating non-ESA missions, i.e. Third Party Missions, into the overall ESA Earth Observation (EO) strategy. Complementary to ESA-owned EO missions, the programme allows European users access to a large portfolio of TPM and is particularly important for promoting the international use of EO data.

The key objective of ESA's EDAP is to take full advantage of the increased range of available data from non-ESA operated missions and to perform an early data assessment for various missions. that fall into one of the following instrument domains:
• VHR, HR and MR Optical Missions
• LR Optical Missions
• SAR missions
• Atmospheric Missions

The present contribution focuses on the assessment of the data quality of third-party SAR missions. The early data assessment is intended to provide some indication of the potential of each existing mission to remain as a TPM. The mission quality assessment is based on specific guidelines and cover the following aspects:
• Data Provider Documentation Review: the assessment covers the products information, metrology and products generation topics. The goal of this assessment is to evaluate the quality of the documentation provided to the users in terms of products formats, generation and calibration; and of the availability and accessibility of the SAR products.
• Independent validation of the data quality by analyzing ad hoc datasets of the third-party missions over calibration sites (e.g., point target calibration sites or Rain Forest) in order to verify the overall data quality in terms of Impulse Response Function characteristics, resolution, radiometric calibration, geolocation accuracy and noise level.

The results of the performed validation are documented in dedicated Technical Notes that are published on the EDAP website (https://earth.esa.int/eogateway/activities/edap/sar-missions). The published TNs include the so-called Mission Quality Assessment Matrix, summarizing in a compact form the results of the performed validation activities.

The following third-party SAR missions have been evaluated so far in the framework of the EDAP project:
• SAOCOM: an L-band SAR constellation made of two satellites operated by the Argentinian space agency (CONAE). The first of two satellites, SAOCOM 1A, was launched on 7 October 2018 into a Sun-synchronous orbit polar orbit, with a 16 day repeat cycle. The same orbit was used for the second satellite, SAOCOM 1B, which was successfully launched on 30 August 2020. The constellation allows a revisit time of 8 days. SAOCOM is the first L-band mission implementing the TopSAR acquisition mode.
• ICEYE: as of the beginning of 2021, the ICEYE constellation consisted of 10 X-band Synthetic Aperture Radar (SAR) satellites. Over the next years, ICEYE will continue to grow its constellation capacity in specialized orbital planes designed to provide persistent monitoring capabilities and high-resolution view of the Earth's surface. Currently, the satellites operate in three modes called 'Strip Mode', 'Spot Mode' and 'Scan Mode'.
• Capella: Capella Space is a U.S. based company, founded in 2016. The company is focused on design and operation of small Synthetic Aperture Radar (SAR) satellites, to monitor the Earth. The Capella satellites operate in the X-band, and can acquire in Spotlight, Sliding Spotlight and Stripmap modes. The constellation provides SAR images with very fine spatial resolution, ranging from 0.5 m up to 1.2 m. The scene coverage goes from 5 x 5 km up to 5 x 20 km.
• PAZ: the PAZ satellite, launched on 22 February 2018, is owned and operated by Hisdesat, and is based on the use of a high-resolution X-band Synthetic Aperture Radar (SAR). The satellite operates in the same orbit of its twin satellites TerraSAR-X and TanDEM-X. The three satellites work together as a constellation. The satellite can operate in Stripmap, ScanSAR, Spotlight and high-resolution Spotlight modes.

The contribution will present the activities performed within the EDAP project and the results of the assessment of the missions reported above.