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  • Important Notification regarding ALOS data provision

Important Notification regarding ALOS data provision


Limitation in Product Provision(ALOS precision orbit data unavailable)

Product provision will be suspended when you order the product with "ALOS precision orbit data only" despite the data is not available.

The data is not available when the data cannot be obtained due to orbit maneuverings in order to maintain proper satellite's trajectory.

Please order products with "most available precise data" to avert this limitation. The scenes (the time of observation) without precision orbit data can be seen "Notice of Lacking ALOS Precision Orbit Data".

About ALOS precision attitude data

Product provision will be suspended when you order the product with "ALOS precision attitude data" despite the data is not available.

The data is not available when the data cannot be obtained to create precision attitude data due to orbit maneuverings for maintaining proper satellite's trajectory.

Please order products with "most available precise data" to avert this limitation. The scenes (the time of observation) without precision attitude data can be seen "Notice of Lacking ALOS Precision Attitude Data".

Rough DEM Correction and its Processing Method

Rough DEM Correction
The rough DEM (Digital Elevation Model) correction is made to compensate the error involved in the location of the observed point. This error appears when observation is performed with some pointing angles (not from right above) and the point observed is elevated. The point observed appears shifted resulting in a wrong latitude/longitude value.
The correction roughly compensates the error using DEM data (currently available only in JAPAN area) and position/attitude of the spacecraft acquired in conventional operations. It is not an ortho-geometric-rectification because it does not make use of GCP (Ground Control Points) to perform precise positional corrections.

Remarks on a Method of Rough DEM Correction
In a Rough DEM Correction for AVNIR-2, the calculation of corrected location may fail when "shadows" of elevated landforms hide some points on the surface if an observation with a large pointing angle is conducted. In such a case, the corrected location is calculated as an average of the surrounding points.

Product Delivery Policy

The type of media will be determined, depending on the requested data volume even if you request a product on a CD-R or DVD-R. Please note that a medium will be delivered with one product on it regardless of your preference.

Cares Recommended before Ordering Products based on Image Catalogs

Scene product may cover an area different from cataloged scene
As our catalog images are made based on predictive orbital data right after the observation, the region covered by a catalog image may differ from that of a product of the same scene. Therefore, a place located near the ends of a catalog image might not stay in the region of the product.
Please confirm that the place of your concern is in a quadrangle defined by the four corner points shown in the table for the scene, the quadrangle is also shown on the map as a scene frame. It is also recommended that you specify a scene shift to locate your place of concern to the center of the scene.
Your understanding is expected that catalog images based on predictive orbit remain as they are while the corner values in the table are updated based on the determinative orbital data basically four days after the observation.

PRISM scene product may be brighter than catalogued scene
Some PRISM products look brighter than their respective catalog images. This is a feature, characteristic of PRISM processing algorithm, exhibited when an area with high reflectivity, such as ice, snow, or desert, is observed using higher gains; where, the processing algorithm tends to give a product brightness higher than its corresponding catalog image. Therefore, some ground traits, which are discernible on a browse may not be distinguished on the product depending on the ground surface conditions.
If you find this feature on your product, please have a contact with our data distribution service.

Cloud Coverage Values in "Search result"

Please note that cloud coverage values in the table shown in "Search result" can be altered within three days after the data acquisition. This happens due to the limited capability of automatic cloud coverage estimation, put in the table, particularly in clouded and snow covered areas. Operators put a visual check to evaluate the cloud coverage within three days.
Please see the following for details.

Automatic cloud coverage evaluation
1. Cloud coverage evaluation is automated to measure the brightness of brows images of PRISM (Nadir view) and/or AVNIR-2 (Band 2, 3, and 4) before performing radiometric correction.
- A PRISM image, having only a single band data, evaluates its cloud coverage by counting the number of pixels brighter than a predetermined threshold value and calculates the relative amount of these pixels to the whole image (this ratio is called cloud quantity reference information).
- An AVNIR-2 image, having plural color bands on the contrary, evaluates its cloud coverage by counting the number of pixels measured not only in brightness but also in hue and color of each pixel to identify clouds.
We have prepared several sets of threshold values to adjust the Automatic evaluation to various seasons and regions. However, certain errors are still involved because images before radiometric correction are applied to this automated cloud coverage evaluation.

2. The automated evaluation fails often with such bright images as of deserts or of snowy/icy areas which resemble clouds in brightness. Visual inspection by an operator is conducted for the images mentioned above in order to avoid such evaluation errors; otherwise, the automatic evaluation tends to give larger values of cloud coverage than visual inspections.

In addition, the automatic cloud coverage evaluation may give a value much different from the way an image looks when the cloud is thin (hazy). In many cases, the automatic evaluation tends to give smaller values of cloud coverage than visual inspections.

Calibration Data

PALSAR sensor conducts calibrating operation right before and after the observational operation. The calibration data include noise measurements, transmission measurements, power measurements, and mode settings of transmitting/receiving wave shapes. When a scene holds these calibration data, the Calibration Flag of the table on AUIG will be shown as "Yes"; however, there remains some cases where a scene holds calibration data even though the corresponding Calibration Flag is "No". If a scene has calibration data, level 1.5 processing will fail with a message disclaiming the calibration data.
For further information of calibration data, refer to fields 11 through 23 of table 3.3-8 Calibration Data Record of "ALOS/PALSAR Level 1.0 Product Format Description".

Range Scene Size of PALSAR Images Reduced

Please be informed that the range scene size of PALSAR products processed at Level 1.1/1.5 will be reduced from July 23, 2007. This modification is applied for the following PALSAR observation modes.

<PALSAR observation modes subject to this modification>
- Fine Beam Mode (FBS, FBD)
- Polarimetry Mode (PLR)
- Direct Downlink Mode (DSN)

Products of PALSAR have been produced with approximately 75 km in the range direction, which includes farther areas than the designed swath width of 70 km, to utilize the acquired data as much as possible. Due to electric signal attenuation, however, ambiguity has frequently appeared, and the resolution has deteriorated at the far range where to be eliminated by this modification. These have caused a misunderstanding that the resolution of PALSAR data is not as high as designed. Therefore, we have decided to reduce the range scene size not to lead further confusion.

As indicated in Figure 1 (a), the left side of the yellow dotted line will not be processed after the modification, and the image will be produced as shown in Figure 1 (b).

This modification will also be applied for images in catalogue information of AUIG.

Figure 1. An example of the image sizes before and after modification

Order for PRISM Images with Blurred Spots

Please note that PRISM images with blurred spots observed after March 21, 2007 will not be listed in AUIG since the characteristic announced as "Blurred Image in PRISM" at "Product characteristics derived from sensor properties" in December 2006 is not appropriate as our products to distribute.

Therefore, the sequence of PRISM images may be incomplete. The unlisted images including blurred spots can be seen "Observation Information for PRISM relating to AVNIR-2 pointing change".

Please be also informed that the images with blurred spots in 4 days after observations are listed and can be ordered. When ordered, the images will be provided as usual products.

Please be aware that there may be some PRISM images with blurred spots when you order PRISM images.

Yaw Steering Status

"Yaw Steering Status" of the scenes (observation date) can be seen in "Yaw Steering ON/OFF history".

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